Sillas appeared in Hal Hartley's 1992 film Simple Men. In 1994, she starred in What Happened Was..., which won the Grand Jury Prize at the Sundance Film Festival and launched Sillas into prime-time television. In CBS's critically acclaimed detective series Under Suspicion, Sillas portrayed Rose Phillips, the only female detective in an otherwise male-dominated squad room. She also starred in several miniseries for television, including Peter Benchley's The Beast with william Petersen.
In the 1998–99 prime-time television season, Sillas appeared on two of CBS's most acclaimed series, Touched by an Angel and Promised Land. She also appeared on the hit HBO series The Sopranos as Debbie.
