Poston, a veteran actor, has been on television since the first flickering images came into living rooms in the 1950s. In a career that goes back to 1950, Poston has appeared as a comic actor, game show panelist, game show host, movie actor, and Broadway performer.

After high school, Poston went to Bethany College in West Virginia but did not graduate. Instead, he joined the United States Army and served with distinction in the European Theater in World War II. Upon his return, he began studying acting in New York City.

In the 1950s, Poston gained fame as a frequent performer on the Steve Allen Show. After the Allen Show, Poston appeared frequently on Broadway and as a game show panelist, including a regular spot on To Tell The Truth. He also played the main character in the movie Zotz.

Poston returned to television as a recurring guest-star on The Bob Newhart Show in the 1970s. He later gained the role of Mr. Bickley on Mork & Mindy. A longtime friend of Bob Newhart, Poston played the role of George Utley, country handyman of the Stratford Inn, on Newhart. He had a third appearance with Newhart in the short lived program Bob.

He has also had recurring roles on many TV series: Family Matters, Murphy Brown, Home Improvement, The Cosby Show, Malcolm & Eddie, ER, and That '70s Show.

In 2001, Poston married actress Suzanne Pleshette who played the wife of Newhart's character Bob Hartley on The Bob Newhart Show.

Today, Poston continues to appear in supporting roles in films, with two new ones released in 2004, Christmas with the Kranks and The Princess Diaries 2: Royal Engagement, and on several television programs.

In 2005, he played the character "Clown" on the briefly aired NBC series Committed.