Lord of the Hightower|
Lord of the Port
Voice of Oldtown
Defender of the Citadel
Beacon of the South
The World of Ice & Fire (mentioned)|
The Sons of the Dragon (mentioned)
Martyn's daughter, Ceryse, was married to Prince Maegor Targaryen in 25 AC, after Ceryse's uncle, the High Septon,[N 1] protested the proposed marriage between Maegor and his cousin, Princess Rhaena Targaryen.
In 43 AC[N 2] when King Maegor, Queen Dowager Visenya, their dragons, and the royal army made their way to Oldtown during the Faith Militant uprising, Lord Martyn called his banners with a fire atop the Hightower. By the morning of their arrival, however, the city gates were open, and the banners of House Targaryen, House Tyrell and House Hightower flew atop the city walls. After word of the sudden death of the High Septon reached him, Lord Martyn at once dispatched his own knights to arrest and disarm all of the Warrior's Sons, including his brother Morgan. Then, Lord Martyn sent his men to rouse the Most Devout from their beds and march them at spearpoint to the Starry Sept to choose a new High Septon.
In 47 AC, Princess Rhaella was made a ward of Lord Martyn when she was sent to Oldtown by King Maegor to be raised as a septa. In the following year when her mother, Queen Rhaena fled from Maegor in the night, Maegor sent a rider to Oldtown commanding Lord Martyn to behead Rhaella as punishment for her mother's betrayal. Lord Martyn refused and imprisoned the messenger instead, he then declared support for Jaehaerys I Targaryen. 
- In The World of Ice & Fire, it is stated that "The unexpected nature of the High Septon's death in 44 AC aroused much suspicion, however, and whispers of murder persist to this day. Some believe His High Holiness was removed by his own brother, Ser Morgan Hightower, commander of the Warrior's Sons in Oldtown (and it is undeniably true that Ser Morgan was the sole Warrior's Son pardoned by King Maegor)." (The World of Ice and Fire, The Reach: Oldtown) However, it has been confirmed that Morgan Hightower was not the High Septon's brother, but that Morgan and Martyn were brothers, and that the printed statement was in error
- Earlier prints of The World of Ice & Fire erroneously state that this event and the death of the High Septon took place in 44 AC (The World of Ice & Fire, The Reach: Oldtown). The Sons of the Dragon gives the correct date of 43 AC. The High Septon elected as a replacement dies a year later, in44 AC.