(written from a Production point of view)
Welsh was well-known for playing the villain, Windom Earle, in the second season of Twin Peaks (1990-91), in which he appeared alongside Mädchen Amick, Richard Beymer, Clarence Williams III, Tony Jay, Catherine Coulson, David Warner, Brenda Strong, Miguel Ferrer, and Carel Struycken. He also played Doctor John H. Watson next to Matt Frewer's Sherlock Holmes in four Hallmark Channel TV movies. He portrayed President Harry S. Truman in the 1995 TV movie Hiroshima, which also featured Ken Jenkins and Saul Rubinek.
His feature film credits included Crocodile Dundee II (1988, with Stephen Root), Timecop (1994, with Bruce McGill and Scott Lawrence), Legends of the Fall (1994), The Day After Tomorrow (2004, with Tamlyn Tomita, Mimi Kuzyk, Sheila McCarthy, and Aaron Lustig), The Aviator (2004, with Brent Spiner), The Fog (2005), 4: Rise of the Silver Surfer (2007, with Doug Jones, Brian Posehn, and Stan Lee), and Silk (2007).
He appeared in guest roles on numberous television series, including Spenser for Hire (co-starring Avery Brooks and directed by Winrich Kolbe), the 1980s reboot of The Twilight Zone, Kung Fu: The Legend Continues, The X-Files (with Michael Berryman), the 1990s version of The Outer Limits (narrated by Kevin Conway), Law & Order, Witchblade, The Practice (with Harve Presnell, Norman Lloyd, Tucker Smallwood), The Murdoch Mysteries, Smallville (with John Glover and Alisen Down), Being Erica, The Expanse (with Shohreh Aghdashloo), and Blacklist (with Enrique Murciano).