Groener's reputation in New York City rests almost entirely on his work in musical theater, although the bulk of his roles outside New York have been in classical drama or contemporary plays like Eastern Standard. His Broadway credits include Is There Life After High School?, Will Parker in Oklahoma!, Munkustrap in Cats, Georges/George in Sunday in the Park with George, and Bobby Child in Crazy for You. In 1999 he performed off-Broadway with Twiggy at the Lucille Lortel Theater in If Love Were All, a musical revue based on the friendship of Noël Coward and Gertrude Lawrence. He has performed in regional theatres across the country, including the San Diego Old Globe Theatre, Mark Taper Forum, Westwood Playhouse, South Coast Repertory, Pasadena Playhouse, Long Wharf Theater, A.C.T., and the Williamstown Theater Festival. Groener has performed regularly on TV, including guest appearances on ', ', and several dozen other series; he was also a series regular on the sitcomDear John. In 1998 and 1999, Groener portrayed Richard Wilkins, the evil mayor of Sunnydale on the third season of cult TV series Buffy the Vampire Slayer. Groener reprised his role in cameo appearances in Buffy's 4th and 7th seasons. From 2003 to 2006 he appeared as the chef Gunther on the TV series Las Vegas. Notable film work includes Road to Perdition and About Schmidt. He also appeared in two episodes of The West Wing as the Secretary of Agriculture and the Bones episode "The Woman at the Airport" as a plastic surgeon, Henry Atlas. In 2009, Groener appeared in the second season episode of Breaking Bad, "Bit by a Dead Bee", as protagonist Walter White's psychiatrist. He also portrayed the role of Clint, Ted's stepdad, in How I Met Your Mother. In January 2018, Groener appeared in the tenth episode of Young Sheldon. He was a regular vocalist for the Varèse Sarabande label, performing on such recordings as Shakespeare on Broadway, Cole Porter: A Musical Toast, and various installments of the Unsung Broadway and Lost in Boston series. He played King Arthur in Monty Python's Spamalot during 2006. In 2010, he appeared as the title role in the Antaeus Company's production of King Lear. He won the L.A. Drama Critics Circle Award for this performance. In 2012 he starred in the debut of Christopher Hampton's play Appomattox at the Guthrie Theater in Minneapolis, playing a dual role as both U.S. President Abraham Lincoln in 1865 and Lyndon B. Johnson in 1965.
