Born in Dakota City, Iowa, Reasoner studied journalism at Stanford University and the University of Minnesota. He served in World War II, coming home later to resume his career with The Minneapolis Times.

After going to radio with CBS in 1948, Reasoner worked for the United States Information Agency in the Philippines. After his return stateside, he went into television working at television station KEYD KMSP in Minneapolis and later moved to New York.

While in New York, Reasoner hosted a morning news program called Calendar on top of doing commentator and special news narration duties.

Reasoner's greatest contribution to television news reporting came in 1968, when he teamed up with Mike Wallace to begin the 60 Minutes newsmagazine series. Reasoner joined ABC in 1970 as co-anchor with Howard K. Smith of the ABC Evening News until 1975 when Reasoner became sole anchor. From 1976 until 1978 Reasoner co-anchored the news with Barbara Walters. Walters and Reasoner did not enjoy a close relationship, due to the fact that Reasoner not only did not like sharing the spotlight with a co-anchor and was uncomfortable with the idea of a female news anchor. The disastrous arrangement ended in 1978. Reasoner returned to CBS and remained at the network until he retired in May 1991.

Reasoner passed away three months later at the age of 68 from a blood clot in the brain received from a fall at his home in Westport, Connecticut. He is interred at Union Cemetery in Humboldt, Iowa.

An editorial cartoon the next day showed Reasoner arriving at the Pearly Gates, with a startled St. Peter crying, "Oh, no! It's 60 Minutes!"

Reasoner didn't mind poking a little fun at his profession. Two of his more cynical comments on journalism:

"Journalism is a kind of profession, or craft, or racket, for people who never wanted to grow up and go out into the real world."

"If you're a good journalist, what you do is live a lot of things vicariously, and report them for other people who want to live vicariously."