Seamus Davey-Fitzpatrick was born on December 29th, 1998 in New York. His father James Fitzpatrick is an actor and model, his mother Marty Davey is an actress. Seamus grew up in New York. The family moved to East Stroudsburg, Pennsylvania, five years ago after looking for an area with a small-town feel.
His mother took young Seamus with her to auditions in New York when he was a baby. So he had his first on-screen appearance at the age of one month, when he portrayed a crack baby in a pitch for a TV pilot. By the age of 4 years Seamus had already acted in commercials for Flintstone Vitamins and Marriott Hotel commercials. He also had an appearance in an episode of the tv series "Sex and the City" as a boy with chocolate in his face.
Seamus attends J.M. Hill Elementary School in East Stroudsburg, where he recently completed the first grade. His favorite subjects are gym and recess. In his spare time he loves soccer and skateboarding.

He made his first appearance on the big screen in the 2006 remake of the movie "The Omen", where he starred besides Julia Stiles, Liev Schreiber and Mia Farrow in the role of "Damien Thorn".
For a callback for The Omen Seamus went to Prague, where the movie was filmed later, for a screen test. He had to swing slowly on a creaky swing. When the director called his name Seamus looked right into the lens of the camera. Moore was so impressed by the scene that he used it as a teaser for the movie.
To his mother Marty Davey that stare is familiar. She told that that is the look he gives her when she tells him to brush his teeth.
For Seamus himself the stare was one of harder tasks of shooting the movie, because he always had to stare at the camera without blinking.
During filming of The Omen, Davey-Fitzpatrick was never told that his character was supposed to be the son of the Devil. He was simply told that he was playing Damien. Co-star Julia Stiles has commented that the filmmakers spared him that because they thought "he was too young to understand it".
Seamus' parents have no problem with the subject of the movie. His mother points out that it is only a movie and it is much more fun to play the bad guy.

Seamus is a happy, talkaktive and very smart child. About himself he says he is 'really shy' and 'a little afraid of the dark'.