Lahti began on Broadway as a replacement in Loose Ends. She went on to perform in the Broadway plays Present Laughter (1982) and The Heidi Chronicles (1989).
Lahti is an eight-time Golden Globe Award nominee and six-time Emmy Award nominee. She won a Golden Globe Award for the 1989 television movieNo Place Like Home. She won a Golden Globe and Emmy in 1998 for her role as Kate Austin in the series Chicago Hope.