diff --git a/packages/perps-controller/CHANGELOG.md b/packages/perps-controller/CHANGELOG.md
index f27bb0297e0..d7064e7f221 100644
--- a/packages/perps-controller/CHANGELOG.md
+++ b/packages/perps-controller/CHANGELOG.md
@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Persist the Isolated/Cross margin-mode pick per market and network in `tradeConfigurations[network][symbol].marginMode`, so clients can restore it after the order form remounts and share it across Mobile and Extension ([#10464](https://github.com/MetaMask/core/pull/10464))
+  - Add `getMarginMode(symbol)` and `saveMarginMode(symbol, marginMode)` methods, exposed as the `PerpsController:getMarginMode` and `PerpsController:saveMarginMode` messenger actions (`PerpsControllerGetMarginModeAction`, `PerpsControllerSaveMarginModeAction`). `saveMarginMode` ignores values other than `isolated` or `cross`.
+  - Add the `selectMarginMode(state, symbol)` selector and an optional `marginMode` field on `TradeConfiguration`.
+
 ## [18.0.1]
 
 ### Fixed
diff --git a/packages/perps-controller/src/PerpsController-method-action-types.ts b/packages/perps-controller/src/PerpsController-method-action-types.ts
index 7c0e6daaa3e..1271dd001d6 100644
--- a/packages/perps-controller/src/PerpsController-method-action-types.ts
+++ b/packages/perps-controller/src/PerpsController-method-action-types.ts
@@ -1271,6 +1271,30 @@ export type PerpsControllerSaveOrderBookGroupingAction = {
   handler: PerpsController['saveOrderBookGrouping'];
 };
 
+/**
+ * Get the saved margin mode (Isolated/Cross) for a market on the current
+ * network. Clients should still let a venue-enforced mode take priority.
+ *
+ * @param symbol - Market symbol
+ * @returns The saved margin mode or undefined if not set
+ */
+export type PerpsControllerGetMarginModeAction = {
+  type: `PerpsController:getMarginMode`;
+  handler: PerpsController['getMarginMode'];
+};
+
+/**
+ * Save the margin mode (Isolated/Cross) picked for a market on the current
+ * network. Values other than `isolated` or `cross` are ignored.
+ *
+ * @param symbol - Market symbol
+ * @param marginMode - Margin mode to persist
+ */
+export type PerpsControllerSaveMarginModeAction = {
+  type: `PerpsController:saveMarginMode`;
+  handler: PerpsController['saveMarginMode'];
+};
+
 /**
  * Toggle watchlist status for a market.
  *
@@ -1463,6 +1487,8 @@ export type PerpsControllerMethodActions =
   | PerpsControllerResetSelectedPaymentTokenAction
   | PerpsControllerGetOrderBookGroupingAction
   | PerpsControllerSaveOrderBookGroupingAction
+  | PerpsControllerGetMarginModeAction
+  | PerpsControllerSaveMarginModeAction
   | PerpsControllerToggleWatchlistMarketAction
   | PerpsControllerIsWatchlistMarketAction
   | PerpsControllerGetWatchlistMarketsAction
diff --git a/packages/perps-controller/src/PerpsController.ts b/packages/perps-controller/src/PerpsController.ts
index 641d05742c4..c53e72205bc 100644
--- a/packages/perps-controller/src/PerpsController.ts
+++ b/packages/perps-controller/src/PerpsController.ts
@@ -105,6 +105,7 @@ import type {
   MaintenanceMarginParams,
   PositionModifyPreviewParams,
   PositionModifyPreviewResult,
+  MarginMode,
   MarginResult,
   MarketInfo,
   Order,
@@ -420,6 +421,7 @@ export type PerpsControllerState = {
       [marketSymbol: string]: {
         leverage?: number; // Last used leverage for this market
         orderBookGrouping?: number; // Persisted price grouping for order book
+        marginMode?: MarginMode; // Last Isolated/Cross pick for this market
         // Pending trade configuration (temporary, expires after 30 seconds)
         pendingConfig?: {
           amount?: string; // Order size in USD
@@ -438,6 +440,7 @@ export type PerpsControllerState = {
       [marketSymbol: string]: {
         leverage?: number;
         orderBookGrouping?: number; // Persisted price grouping for order book
+        marginMode?: MarginMode; // Last Isolated/Cross pick for this market
         // Pending trade configuration (temporary, expires after 30 seconds)
         pendingConfig?: {
           amount?: string; // Order size in USD
@@ -925,6 +928,7 @@ const MESSENGER_EXPOSED_METHODS = [
   'getMarketDataWithPrices',
   'getMarketFilterPreferences',
   'getMarkets',
+  'getMarginMode',
   'getMaxLeverage',
   'getOpenOrders',
   'getOrderBookGrouping',
@@ -967,6 +971,7 @@ const MESSENGER_EXPOSED_METHODS = [
   'setProLayoutPreferences',
   'setPerpsMode',
   'setSelectedOrderType',
+  'saveMarginMode',
   'saveMarketFilterPreferences',
   'saveOrderBookGrouping',
   'savePendingTradeConfiguration',
@@ -6727,6 +6732,51 @@ export class PerpsController extends BaseController<
     });
   }
 
+  /**
+   * Get the saved margin mode (Isolated/Cross) for a market on the current
+   * network. Clients should still let a venue-enforced mode take priority.
+   *
+   * @param symbol - Market symbol
+   * @returns The saved margin mode or undefined if not set
+   */
+  getMarginMode(symbol: string): MarginMode | undefined {
+    const network = this.state.isTestnet ? 'testnet' : 'mainnet';
+    return this.state.tradeConfigurations[network]?.[symbol]?.marginMode;
+  }
+
+  /**
+   * Save the margin mode (Isolated/Cross) picked for a market on the current
+   * network. Values other than `isolated` or `cross` are ignored.
+   *
+   * @param symbol - Market symbol
+   * @param marginMode - Margin mode to persist
+   */
+  saveMarginMode(symbol: string, marginMode: MarginMode): void {
+    if (marginMode !== 'isolated' && marginMode !== 'cross') {
+      return;
+    }
+
+    const network = this.state.isTestnet ? 'testnet' : 'mainnet';
+
+    this.#debugLog('PerpsController: Saving margin mode', {
+      symbol,
+      network,
+      marginMode,
+    });
+
+    this.update((state) => {
+      if (!state.tradeConfigurations[network]) {
+        state.tradeConfigurations[network] = {};
+      }
+
+      const existingConfig = state.tradeConfigurations[network][symbol] || {};
+      state.tradeConfigurations[network][symbol] = {
+        ...existingConfig,
+        marginMode,
+      };
+    });
+  }
+
   /**
    * Toggle watchlist status for a market.
    *
diff --git a/packages/perps-controller/src/index.ts b/packages/perps-controller/src/index.ts
index e97b7f34822..75afd7d8060 100644
--- a/packages/perps-controller/src/index.ts
+++ b/packages/perps-controller/src/index.ts
@@ -97,6 +97,7 @@ export type {
   PerpsControllerGetMarketFilterPreferencesAction,
   PerpsControllerGetMarketCategoriesAction,
   PerpsControllerGetMarketsAction,
+  PerpsControllerGetMarginModeAction,
   PerpsControllerGetMaxLeverageAction,
   PerpsControllerGetOpenOrdersAction,
   PerpsControllerGetOrderBookGroupingAction,
@@ -131,6 +132,7 @@ export type {
   PerpsControllerRefreshEligibilityAction,
   PerpsControllerResetFirstTimeUserStateAction,
   PerpsControllerResetSelectedPaymentTokenAction,
+  PerpsControllerSaveMarginModeAction,
   PerpsControllerSaveMarketFilterPreferencesAction,
   PerpsControllerGetProLayoutPreferencesAction,
   PerpsControllerSetProLayoutPreferencesAction,
@@ -705,6 +707,7 @@ export {
   selectPendingTradeConfiguration,
   selectMarketFilterPreferences,
   selectOrderBookGrouping,
+  selectMarginMode,
   selectOrderBookPreferences,
   selectProLayoutPreferences,
   selectSelectedOrderType,
diff --git a/packages/perps-controller/src/selectors.ts b/packages/perps-controller/src/selectors.ts
index 3677988fb1d..2566d56983f 100644
--- a/packages/perps-controller/src/selectors.ts
+++ b/packages/perps-controller/src/selectors.ts
@@ -17,6 +17,7 @@ import type {
 } from './constants/perpsConfig.js';
 import type { PerpsControllerState } from './PerpsController.js';
 import type {
+  MarginMode,
   OrderDirection,
   OrderType,
   PerpsSelectedPaymentToken,
@@ -363,3 +364,28 @@ export const selectOrderBookGrouping = createSelector(
     return configs?.[network]?.[coin]?.orderBookGrouping;
   },
 );
+
+/**
+ * Select the saved margin mode for a specific market on the current network.
+ *
+ * Usage: selectMarginMode(state, coin)
+ *
+ * @param state - The perps controller state.
+ * @param coin - The market coin symbol.
+ * @returns The saved margin mode, or undefined.
+ */
+export const selectMarginMode = createSelector(
+  [
+    (state: PerpsControllerState): boolean | undefined => state?.isTestnet,
+    (
+      state: PerpsControllerState,
+      _coin: string,
+    ): PerpsControllerState['tradeConfigurations'] | undefined =>
+      state?.tradeConfigurations,
+    (_state: PerpsControllerState, coin: string): string => coin,
+  ],
+  (isTestnet, configs, coin): MarginMode | undefined => {
+    const network = isTestnet ? 'testnet' : 'mainnet';
+    return configs?.[network]?.[coin]?.marginMode;
+  },
+);
diff --git a/packages/perps-controller/src/types/index.ts b/packages/perps-controller/src/types/index.ts
index e253b8bfa8a..0a4aecc4f1f 100644
--- a/packages/perps-controller/src/types/index.ts
+++ b/packages/perps-controller/src/types/index.ts
@@ -70,6 +70,7 @@ export type GetUserHistoryParams = {
 // Trade configuration saved per market per network
 export type TradeConfiguration = {
   leverage?: number; // Last used leverage for this market
+  marginMode?: MarginMode; // Last Isolated/Cross pick for this market
   // Pending trade configuration (temporary, expires after 30 seconds)
   pendingConfig?: {
     amount?: string; // Order size in USD
diff --git a/packages/perps-controller/tests/src/PerpsController.configuration.test.ts b/packages/perps-controller/tests/src/PerpsController.configuration.test.ts
index 34826c15fa5..c6161a7dbc1 100644
--- a/packages/perps-controller/tests/src/PerpsController.configuration.test.ts
+++ b/packages/perps-controller/tests/src/PerpsController.configuration.test.ts
@@ -43,6 +43,7 @@ import { HyperLiquidProvider } from '../../src/providers/HyperLiquidProvider.js'
 import type {
   AccountState,
   GetAvailableDexsParams,
+  MarginMode,
   PerpsProvider,
   PerpsPlatformDependencies,
   PerpsProviderType,
@@ -1503,6 +1504,81 @@ describe('PerpsController', () => {
     });
   });
 
+  describe('margin mode', () => {
+    it('saves margin mode for mainnet', () => {
+      controller.testUpdate((state) => {
+        state.isTestnet = false;
+      });
+
+      controller.saveMarginMode('BTC', 'cross');
+
+      expect(controller.getMarginMode('BTC')).toBe('cross');
+      expect(controller.state.tradeConfigurations.mainnet.BTC).toStrictEqual({
+        marginMode: 'cross',
+      });
+    });
+
+    it('saves margin mode for testnet without touching mainnet', () => {
+      controller.testUpdate((state) => {
+        state.isTestnet = true;
+      });
+
+      controller.saveMarginMode('ETH', 'isolated');
+
+      expect(controller.getMarginMode('ETH')).toBe('isolated');
+      expect(controller.state.tradeConfigurations.mainnet.ETH).toBeUndefined();
+    });
+
+    it('returns undefined when no margin mode is saved', () => {
+      expect(controller.getMarginMode('SOL')).toBeUndefined();
+    });
+
+    it('overwrites the previous margin mode for the same market', () => {
+      controller.saveMarginMode('BTC', 'cross');
+      controller.saveMarginMode('BTC', 'isolated');
+
+      expect(controller.getMarginMode('BTC')).toBe('isolated');
+    });
+
+    it('preserves existing config when saving margin mode', () => {
+      controller.testUpdate((state) => {
+        state.isTestnet = false;
+      });
+      controller.saveTradeConfiguration('BTC', 5);
+      controller.saveOrderBookGrouping('BTC', 100);
+
+      controller.saveMarginMode('BTC', 'cross');
+
+      expect(controller.getTradeConfiguration('BTC')?.leverage).toBe(5);
+      expect(controller.getOrderBookGrouping('BTC')).toBe(100);
+      expect(controller.getMarginMode('BTC')).toBe('cross');
+    });
+
+    it('ignores values that are not a margin mode', () => {
+      controller.saveMarginMode('BTC', 'cross');
+
+      controller.saveMarginMode('BTC', 'portfolio' as MarginMode);
+
+      expect(controller.getMarginMode('BTC')).toBe('cross');
+    });
+
+    it('exposes margin mode methods as messenger actions', async () => {
+      const messenger = createMockMessenger();
+      const localController = new TestablePerpsController({
+        messenger,
+        state: getDefaultPerpsControllerState(),
+        infrastructure: mockInfrastructure,
+      });
+
+      await localController.init();
+
+      expect(messenger.registerMethodActionHandlers).toHaveBeenCalledWith(
+        localController,
+        expect.arrayContaining(['getMarginMode', 'saveMarginMode']),
+      );
+    });
+  });
+
   describe('standalone mode', () => {
     const mockUserAddress = '0xabcdef1234567890abcdef1234567890abcdef12';
     const MockedHyperLiquidProvider = HyperLiquidProvider as jest.MockedClass<
diff --git a/packages/perps-controller/tests/src/selectors.test.ts b/packages/perps-controller/tests/src/selectors.test.ts
index 7f1da6193b4..0e4c784763f 100644
--- a/packages/perps-controller/tests/src/selectors.test.ts
+++ b/packages/perps-controller/tests/src/selectors.test.ts
@@ -13,6 +13,7 @@ import {
   selectHasPlacedFirstOrder,
   selectMarketFilterPreferences,
   selectOrderBookGrouping,
+  selectMarginMode,
   selectRecentlyViewedMarkets,
   selectProLayoutPreferences,
   selectOrderBookPreferences,
@@ -612,6 +613,45 @@ describe('PerpsController selectors', () => {
     });
   });
 
+  describe('selectMarginMode', () => {
+    it('returns the mainnet margin mode when not on testnet', () => {
+      const state = {
+        isTestnet: false,
+        tradeConfigurations: {
+          mainnet: { BTC: { marginMode: 'cross' } },
+          testnet: { BTC: { marginMode: 'isolated' } },
+        },
+      } as unknown as PerpsControllerState;
+
+      expect(selectMarginMode(state, 'BTC')).toBe('cross');
+    });
+
+    it('returns the testnet margin mode when on testnet', () => {
+      const state = {
+        isTestnet: true,
+        tradeConfigurations: {
+          mainnet: { BTC: { marginMode: 'cross' } },
+          testnet: { BTC: { marginMode: 'isolated' } },
+        },
+      } as unknown as PerpsControllerState;
+
+      expect(selectMarginMode(state, 'BTC')).toBe('isolated');
+    });
+
+    it('returns undefined when margin mode is not set', () => {
+      const state = {
+        isTestnet: false,
+        tradeConfigurations: {
+          mainnet: { BTC: { leverage: 10 } },
+          testnet: {},
+        },
+      } as unknown as PerpsControllerState;
+
+      expect(selectMarginMode(state, 'BTC')).toBeUndefined();
+      expect(selectMarginMode(state, 'SOL')).toBeUndefined();
+    });
+  });
+
   describe('selectRecentlyViewedMarkets', () => {
     const now = Date.now();
     const withinTtl = now - 60 * 60 * 1000; // 1 hour ago — within 24h TTL