Trelawny then travelled to Greece with Lord Byron in order to fight in the Greek War of Independence. Byron and Trelawny split up near Greece and Trelawny travelled into Greece to act as the agent of Lord Byron. After Byron died, Trelawny oversaw the preparations for the funeral and the return of his body to England. He also wrote his obituaries. Trelawny joined the cause of the Greek Revolutionary Odysseas Androutsos and helped to provide him with additional arms. He also married Odysseas' sister Tarsitsa. After Odysseas fell out of favour with the Greek government and was arrested, Trelawny took control of his mountain fortress. During this time, Trelawny survived an assassination attempt. After leaving Greece, he divorced Tarsitsa and returned to England. In England he was well received by members of London society. He then wrote a memoir titled "Adventures of a Younger Son". After the book was published he travelled to America for two years before returning to England. He then became politically active but soon remarried and moved to the English countryside.