- In the 1978 film adpatation, he was portrayed by the late Simon MacCorkindale.
- In the 2004 adapation included in ITV's series, Agatha Christie's Poirot, he was portrayed by JJ Feild, who later portrayed the culprit of The Pale Horse in Agatha Christie's Marple.
- In the upcoming 2020 film adaptation, he will be portrayed by Armie Hammer, who also voiced Jackson Storm in Cars 3 and Steve Lift in Sorry to Bother You.
Simon Doyle was the ex-lover of Jacqueline de Bellefort and was later married to the latter's former best friend, Linnet Doyle, after she stole him from Jacqueline. Nevertheless, Simon was revealed to be still in love with Jacqueline and hated Linnet for parting them. As a result, Simon joined Jacqueline's vengeful scheme to kill off Linnet and steal her fortune, first through staging their break-up and then through murder attempts.
On the night of the murder, Jacqueline's shot deliberately missed Simon, who faked his injury with red ink. While everyone in the lounge was distracted by Jacqueline, he took her gun that she had deliberately discarded, went to Linnet's cabin, and shot her. He then returned to the lounge and shot his own leg, to give himself a genuine injury.
However, his action was witnessed by Louise Bourget, the maid of Linnet, who used it to blackmail Simon. Louise's action soon got herself killed by Jacqueline, an act witnessed by Mrs. Otterbourne who was murdered again by Jacqueline before she could warn Poirot.
At the climax of the story, Poirot stayed alone with Simon and revealed what led him to his theory: the ink was contained in a bottle of nail polish he noticed in Linnet's cabin. Simon reloaded the gun with two spare cartridges before he disposed of it, as Poirot realized that three shots were fired that night; the stole was used to silence the gun when Simon shot his own leg.
Poirot suspected premeditation for the murder, because he slept deeply through that night's events – he had been drugged through his wine that evening. After the revealtion, both Simon and Jacqueline admitted their deeds.
The next day, as the cruise reached Cairo, Jacqueline shoots Simon and herself dead with another gun she possessed, so they may escape the gallows. Poirot knew Jacqueline had a second gun all along, but allowed her to commit murder-suicide out of sympathy towards them.
- Since Jacqueline killed Simon before her suicide, Simon is the novel's fourth and final victim.