An affable and appealing brown-haired performer with a charming girl-next-door cuteness and zany comic ability, Jillian Bach began her acting career with guest stints on TV series and a cameo in the popular teen comedy "American Pie" (1999) before landing a regular role on the ABC sitcom "Two Guys and a Girl". Following up a 1998 turn on The WB's college drama "Felicity" with turns on the network's sitcom "Zoe, Duncan Jack and Jane" (1999) as well as Fox's "The X-Files" (also 1999) and "Party of Five" (2000).

In early 1999, Bach debuted on the then-titled "Two Guys, a Girl and a Pizza Place" with a one-off turn as a character named Jamie. Later that year she created the role of Irene, the humorously obsessed ex-girlfriend of "Guy" Pete (Richard Ruccolo) on the revamped "Two Guys and a Girl". Bach played this cat-hoarding, busybody neighbor in a recurring capacity for the 1999-2000 season and was made a regular on the series in the fall of 2000, bringing her wacky comedic portrayal of the somewhat psychotic Irene to the screen with more storylines, including an ongoing secret rendezvous with the other, more arrogant "Guy" Berg (Ryan Reynolds).