For more than 30 years, he introduced the show with a drawn-out "Heeeeeeeeeeeeeere's Johnny!". His booming voice and constant laughter earned him the nickname the Human Laugh Track.

He later also became well-known as the presenter of American Family Publishers sweepstakes (not to be confused with Publishers Clearing House) who arrives unannounced at the homes of winners. He subsequently made a series of Neighborhood Watch PSAs (Public Service Announcements) reprising that role in parody.

He also hosted the long-running syndicated talent show Star Search, cohosted the Jerry Lewis Labor Day Telethon, emceed the game shows Snap Judgment, Concentration and Who Dunnit?, and performed in numerous television commercials, most notably for Budweiser.

In the 1970s and 80s, he anchored the team of NBC personalities covering the network's coverage of the Macy's Thanksgiving Day Parade.

McMahon has appeared in several films, including The Incident (1967), Fun With Dick and Jane (1976), Full Moon High (1981) and Butterfly (1982), and, lastly, in a brief bit in the film version of the old TV series Bewitched (2005), which starred Nicole Kidman.

McMahon began his career as a bingo caller in Maine, when he was fifteen. He worked as a carnival barker for three years as a teenager, and put himself through college as a pitchman for vegetable slicers on the Atlantic City boardwalk.

He attended The Catholic University of America where he joined the Phi Kappa Theta fraternity. He graduated with a Bachelor of Arts in 1949.

During World War II he was decorated as a Marine fighter pilot, and also served as a flight instructor and test pilot. He continued his military career in 1952 by flying 85 missions in Korea, and rose to the rank of full Colonel in the Marines, then was commissioned as Brigadier General in the California Air National Guard, a fact confirmed by John Garofalo but not believed due to his earlier proclivity towards exaggeration.

Several of his ancestors, including the Marquis d'Equilly, also had long and distinguished military careers. A McMahon was a Marshall of armies in France and served under Napoleon III. McMahon also once asserted to Johnny Carson that an ancestor of his had something to do with the invention of the salad dressing known as mayonnaise (from the County Mayo origins of his ancestor).

Since the origin of mayonnaise is unclear, it is also unclear if he was being sincere or just being funny.

McMahon served on the boards of The Marine Corps Scholarship Fund, the Horatio Alger Association, and St. Jude's Ranch for Children, located in Boulder City, Nevada.

He was named honorary chairman of the National Marine Corps Aviation Museum to be built at Cherry Point, North Carolina. He also was President of the Catholic University Alumni Association for four years.

In the 1990's, McMahon was considered one of the richer members of the Hollywood set with substantial investments in real estate (one of the largest landlords in Malibu), and in diversified brewing stocks. He was reputed to be worth in excess of $200 million in real estate holdings and real estate partnerships, although his net worth declined somewhat, just like Johnny Carson, due to several divorce settlements.

In 1986 "Weird Al" Yankovic wrote a tribute song titled "Here's Johnny".

From 1997 to 1998 he appeared in the situation comedy, The Tom Show, starring Tom Arnold.

In 2004, he became the announcer and co-host of Alf's Hit Talk Show on TV Land.

As part of the introductory patter to The Tonight Show Starring Johnny Carson, McMahon would state his name out loud, pronouncing it as Ed "Mc MAH yon", but neither his long-time cohort Johnny Carson nor seemingly anyone else who interviewed him ever seemed to pick up on that subtlety, usually referring to him as Ed "Mc MAN".

The extroverted McMahon made a good counter to the notoriously shy Carson. Nonetheless, McMahon once told an interviewer that after his many decades as an emcee, he would still get "butterflies" in the stomach every time he would walk onto a stage.

He said that instead of letting that nervousness defeat him, he would use it as "energy" for his role as emcee.

Recently, McMahon sued and won a substantial lawsuit related to toxic mold that overtook his home and ruined his priceless memorabilia collection.

He has just authored a memoir recounting his decades long relationship with Johnny Carson.