diff --git a/components/brave_wallet/browser/json_rpc_service.cc b/components/brave_wallet/browser/json_rpc_service.cc
index cc6588ef8add..42a7abce21b3 100644
--- a/components/brave_wallet/browser/json_rpc_service.cc
+++ b/components/brave_wallet/browser/json_rpc_service.cc
@@ -297,7 +297,21 @@ void JsonRpcService::UpdateIsEip1559(const std::string& chain_id,
   if (error != mojom::ProviderError::kSuccess)
     return;
 
+  // Disable EIP-1559 on selected networks, by overwriting is_eip1559 to
+  // false.
+  //
+  // This list needs to be updated until we have a generic EIP-1559 gas
+  // oracle. See: https://github.com/brave/brave-browser/issues/20469.
+  if (chain_id == "0x13881" ||  // Polygon Mumbai Testnet
+      chain_id == "0x89" ||     // Polygon Mainnet
+      chain_id == "0xa86a" ||   // Avalanche Mainnet
+      chain_id == "0xa869"      // Avalanche Fuji Testnet
+  ) {
+    is_eip1559 = false;
+  }
+
   bool changed = false;
+
   if (chain_id == brave_wallet::mojom::kLocalhostChainId) {
     changed = prefs_->GetBoolean(kSupportEip1559OnLocalhostChain) != is_eip1559;
     prefs_->SetBoolean(kSupportEip1559OnLocalhostChain, is_eip1559);
diff --git a/components/brave_wallet/browser/json_rpc_service_unittest.cc b/components/brave_wallet/browser/json_rpc_service_unittest.cc
index 397a63a9ee30..f464f30479bd 100644
--- a/components/brave_wallet/browser/json_rpc_service_unittest.cc
+++ b/components/brave_wallet/browser/json_rpc_service_unittest.cc
@@ -1386,6 +1386,41 @@ TEST_F(JsonRpcServiceUnitTest, UpdateIsEip1559CustomChain) {
   EXPECT_FALSE(GetIsEip1559FromPrefs(chain2.chain_id));
 }
 
+TEST_F(JsonRpcServiceUnitTest, UpdateIsEip1559DisablePolygon) {
+  std::vector<base::Value> values;
+
+  // Define EthereumChain for Polygon network with is_eip1559 set to true.
+  brave_wallet::mojom::EthereumChain polygon(
+      "0x89", "Polygon Mainnet", {"https://url.com"}, {"https://url.com"},
+      {"https://url.com"}, "Polygon Matic", "MATIC", 18, true);
+  auto polygon_ptr = polygon.Clone();
+  values.push_back(brave_wallet::EthereumChainToValue(polygon_ptr));
+
+  UpdateCustomNetworks(prefs(), &values);
+
+  // Expected is_eip1559 should always be false for Polygon.
+  TestJsonRpcServiceObserver observer(polygon.chain_id, false);
+  json_rpc_service_->AddObserver(observer.GetReceiver());
+
+  // Switching to Polygon should update is_eip1559 to false, even if it
+  // was previously set to true.
+  EXPECT_TRUE(GetIsEip1559FromPrefs(polygon.chain_id));
+  SetIsEip1559Interceptor(true);
+  SetNetwork(polygon.chain_id);
+  EXPECT_TRUE(observer.chain_changed_called());
+  EXPECT_TRUE(observer.is_eip1559_changed_called());
+  EXPECT_FALSE(GetIsEip1559FromPrefs(polygon.chain_id));
+
+  // Switching to Polygon again should not call observer methods for change
+  // in is_eip1559.
+  observer.Reset(polygon.chain_id, false);
+  SetIsEip1559Interceptor(true);
+  SetNetwork(polygon.chain_id);
+  EXPECT_TRUE(observer.chain_changed_called());
+  EXPECT_FALSE(observer.is_eip1559_changed_called());
+  EXPECT_FALSE(GetIsEip1559FromPrefs(polygon.chain_id));
+}
+
 TEST_F(JsonRpcServiceUnitTest, GetEthAddrInvalidDomain) {
   const std::vector<std::string> invalid_domains = {"", ".eth", "-brave.eth",
                                                     "brave-.eth", "b.eth"};