During the 1990s, Sills built a reputation as a stage character actor, especially in the professional theaters of southern California. He also performed in several national tours, including Into the Woods and The Secret Garden, which would also feature future Broadway stars as James Stacy Barbour and Audra McDonald. He met his partner, Todd, in 1994 while touring with The Secret Garden.[6] His first Broadway role, however, came when composer Frank Wildhorn and lyricist Nan Knighton approached him in hopes of finding a male lead for their new musical, The Scarlet Pimpernel. Before this audition, Sills told his agent not to send him to any more auditions because he planned to attend law school. With a score in the 99th percentile on the Law School Admission Test (LSAT), Sills hoped to attend Stanford Law School. However, being a fan of the movie as a child, Sills decided to give acting one more chance and was offered the lead as Sir Percy Blakeney.[7]
Douglas Sills opened in his first Broadway show on November 9, 1997. Continuing the role in three other versions of the show, Sills received a Tony Award nomination. He portrayed the foppish hero in SP 1.0 (The Original Broadway Production, starring Terrence Mann, Christine Andreas and Gilles Chiason), SP 2.0 (the revised Broadway production, starring Rachel York and Rex Smith), and for several months in the national tour.[8][9] Although rumored as playing the title role in Wildhorn's Dracula, the Musical, Sills opted out (despite doing a recording demo), and Tom Hewitt portrayed the gothic character at the premiere at the La Jolla Playhouse in 2001.[citation needed] He played Orin Scrivello and several other roles in the 2003 Broadway revival cast of Little Shop of Horrors.[10]
In 2004, Sills joined the Broadway-bound Chicago production of Monty Python's Spamalot.[11] However, before the production began, Sills left due to reported "major script changes."[12] In early 2005, production plans were announced for Wildhorn's new musical Cyrano de Bergerac, from the same team that helped launch his career with The Scarlet Pimpernel.[13] The title role was written specifically for Sills,[14] however, producers dropped plans for the show in spring 2006 without explanation. A studio-concept recording was planned, starring Sills, Linda Eder and Rob Evan, but plans for it also quickly fell through.
In 2009, Sills starred opposite Kristin Chenoweth at the Encores!New York City Center production of Music in the Air, a long-forgotten Kern-Hamerstein musical from the 1930s. The concert-style version ran February 5 through February 8.[15] Sills assumed the role of Gomez Addams in the national tour of The Addams Family in September 2011 until the company's closing on December 30, 2012.[16]
Sills appeared on Broadway beginning in April 2015, playing an aging orchestra conductor in the comedy Living on Love, written by Joe DiPietro, starring Renee Fleming, Jerry O'Connell and Anna Chlumsky.[19]
He appeared in the new musical Dave at the Arena Stage in Washington, D.C., in 2018, in the role of Chief of Staff Bob Alexander. The musical has music by Tom Kitt, lyrics by Nell Benjamin, and the book by Benjamin and Thomas Meehan and is based on the 1993 film Dave.[20]
As of 2022, Sills plays Monsieur Baudin in HBO's The Gilded Age.