The following are known Action Replay Codes for The Lord of the Rings: The Third Age on Nintendo Game Boy Advance (GBA).
These codes were also known as GameShark Codes and in most cases will work on both devices.

These codes are for the U.S. version of the game.

Master Code – Must Be On
aaa1effd
969d0712
7990f320
469ebee5

Always Your Turn
23007233
f2c1f58d
72e45956
8d5ff305
e50a117b
c895b37b
7d1b8632
bbae5f0f
1e27d83b
bbfb6923
08dbc3d9
4f426bd6
08b1b9d3
1e68bf89
04e31125
b3bab1ef
b9c9ef70
3e3e92a7
1e27d83b
bbfb6923

Infinite EXP
695911ec
05750ab3
cf830ff5
47290182