The young actor was soon headlining his own sitcom, playing unassuming college freshman Steven Karp on the Fox sitcom "Undeclared". Evoking the unabashed enthusiasm and heartbreaking humility of his character—a reformed high school nerd looking to become somebody in college—Baruchel brought Steven to life with the right combination of energy, innocence and charm. Picked up for a season, the series found consistent viewers, making the actor a familiar face in many homes. It was canceled, however, after the first season—its niche audience was unable to sustain the show’s life.

On the heels of a newfound celebrity, Baruchel co-starred with fellow television stars James Van Der Beek and Jessica Biel in Roger Avary's adaptation of author Bret Easton Ellis' "Rules of Attraction" (2002). A satire about wealthy, hedonistic college students, “Rules of Attraction” failed to seduce critics and audiences. After starring in the an unaired sitcom pilot for Fox, “The Robinson Brothers”, Baruchel turned in a poignant comic performance as a hapless wannabe boxer, Danger Barch, in “Million Dollar Baby” (2004), an exquisite and subtle drama directed by Clint Eastwood. Co-starring Hilary Swank and Morgan Freeman, “Million Dollar Baby” earned mention in numerous top ten lists for the year and a few Golden Globe nominations—including Best Picture—and was a strong contender for several Oscar nods.