McMahon's first appearance before a microphone was as a 15 year old "caller" at a bingo game in Maine. After that he would spend the next 3 years touring the state fair and carnival circuit. A fighter pilot during World War II, McMahon sold vegetable slicers on Atlantic City's boardwalk to put himself through Catholic University in Washington D.C.. In the 1950s, McMahon hosted a late-night interview show in Philadelphia before working as a clown on the show "Big Top". His next assignment was as fighter pilot during the Korean War. After that he resumed his career in Television. In 1959, he was hired as Johnny Carson's straight man on the daytime quiz show "Who Do You Trust?" When Carson succeeded Jack Paar on NBC's Tonight Show, he took McMahon with him. This job would last for 30 years and make McMahon wealthy and famous. On the big screen he would play straight roles in the dramatic 'The Incident (1967)', and in the comic 'Fun with Dick and Jane (1977)'. He would also appear in Television Movies and host daytime game shows in the sixties and seventies. In the eighties, McMahon would team with Dick Clark on "Bloopers and Practical Jokes", and host his own long-running talent show, "Star Search". He would also make commercial appearances for a multitude of products. In 1994, he would be cast as Ed McMahon in 'Love Affair' with Benning and Beatty.


Was a decorated Marine fighter pilot during WWII. 'Weird Al' Yankovic wrote a song about him called "Here's Johnny". Retired as a Colonel in the United States Marine Corps. During World War II, he was a pilot-instructor and test pilot. During the Korean War, he flew 85 combat missions after being called back to active service in 1952. Was commissioned a Brigadier General in the California Air National Guard in 1966 and continued to serve after he began his acting career. Along with James Stewart, he held the highest active military rank of any actor in history. McMahon was the highest-ranking officer to become an actor, and Stewart was the established actor who achieved the highest rank. Both were decorated combat aviators. Was present for the 2007 demolishing of the old Burbank studio where he had taped the last "The Tonight Show Starring Johnny Carson" (1962), calling it an end of an era. Hospitalized in intensive care in a Los Angeles for treatment of pneumonia and bone cancer [February 27, 2009]. Father of Claudia McMahon.