He was commissioned to join NBC's Saturday Night Live as a cast member in 1998, fulfilling a lifelong dream. Fallon remained on SNL for six years between 1998 and 2004, co-hosting the program's Weekend Update segment and becoming a celebrity in the process. He left the program for the film industry, starring in films such as Taxi (2004) and Fever Pitch (2005).
Following his film career, Fallon returned to television as the host of Late Night with Jimmy Fallon on NBC in 2009, where he became well known for his emphasis on music and games. He moved from that program to become the sixth permanent host of the long-running The Tonight Show in 2014. In addition to his television work, Fallon has released two comedy albums and five books.
James Thomas Fallon was born in the Bay Ridge neighborhood of Brooklyn, New York on September 19, 1974, the son of Gloria (née Feeley) and James W. Fallon. He is of German, Irish, and Norwegian descent. His paternal grandmother, Luise Schalla, was a German immigrant from Osterholz-Scharmbeck, while one of his maternal great-grandfathers, Hans Hovelsen, was a Norwegian immigrant from Fredrikstad. Another set of great-great-grandparents were Thomas Fallon, an Irishman from County Galway, and Louisa Stickever, the daughter of an Irishman born in France and his Irish wife.
A Vietnam War veteran, Fallon's father spent his adolescence singing in street-corner doo-wop groups. Shortly after his son's birth, he started working as a machine repairman for IBM in Kingston, New York. In preparation, the family relocated nearby to Saugerties, New York. Fallon has described his childhood as "idyllic", while his parents have been noted as overprotective. He and his sister, Gloria, were unable to leave their home and had to ride their bicycles in the backyard. Fallon attended the Roman Catholic school St. Mary of the Snow. He considered being a priest, inspired by his experiences as an altar boy, but became more interested in comedy instead. He spent many nights recording the radio program The Dr. Demento Show on a reel-to-reel recorder, which exposed him to both comedy and music.
As a teenager, Fallon developed an obsession with the late-night comedy program Saturday Night Live, watching it religiously. He grew up watching the show, viewing "the clean parts" that his parents taped for him. He and Gloria would re-enact sketches like "The Festrunk Brothers" with friends. Fallon was such a fan that he made a weekly event of watching the show in his dormitory during college. In his teens, he impressed his parents with different impersonations, including actor James Cagney and comedian Dana Carvey. He was also musically inclined, and started playing guitar at age 13. He would go on to perform comedy and music in contests and shows. By his junior high years, he was labeled a class clown, to his teachers' dismay, but was also described as "nice and well-mannered".