Middleton's first step toward acting was signing up for a $15 acting class with friends at a
California junior college. He made his film debut in the 1983 TV movie,
Miss Lonelyhearts. In 1997, Middleton wrote the one-person play,
Miracle Mile, about his lifelong struggle with
juvenile rheumatoid arthritis. He performed it in New York City and other parts of the US. In the 1990s, Middleton had a recurring role on
Law & Order as
forensics technician, Ellis. He also played a recurring character known as Edward Markham, a
rare book dealer, in the science-fiction series,
Fringe. Middleton appeared as a recurring cast member on
The Blacklist in which he played Glen Carter, a DMV worker who moonlights as a tracker. This is arguably his most well-known role. In 2017, he was cast as Charlie,
Audrey Horne's husband, in the
Showtime Network series,
Twin Peaks: The Return, the sequel to the 1990s TV series,
Twin Peaks. His final performance, via
Zoom, was in July 2020. He played a weary Times Square hotel night clerk in Eugene O'Neill's one-act play,
Hughie. He performed it from his bedroom. Following Middleton's death, his character Glen also died of
West Nile virus in The Blacklist (season 8) episode 6, "The Wellstone Agency." The episode was dedicated to Middleton, and featured
Huey Lewis playing himself as part of the character's memorial. ==Personal life==