The show was originally about a divorced woman. Divorce was still a hot subject in 1970, so it changed to a broken engagement. The network was afraid people would think that Mary Tyler Moore had divorced Rob Petrie, her character's husband on The Dick Van Dyke Show (1961).
According to a 2013 interview with Valerie Harper and Cloris Leachman on the TV show "The Doctors," this show was the first (scripted) show in TV history ever to use the word "gay" to refer to homosexuality (in the season three episode "My Brother's Keeper") when Rhoda tells Phyllis that Phyllis's brother is gay.
When the famous opening credit sequence was reworked for Season 3-4, the Mary crew was being followed by a news team for the talk show program "Moore on Sunday". Both the news crew and the police officer escorting the Mary team were pressed into service for one of the clips (when the Mary Richards character has to duck to avoid being caught on film as the "news" cameraman swings his camera around in the direction the officer points).
In the opening credits, the two joggers who pass Mary in the park are producers James L. Brooks and Allan Burns. The gray-haired man Mary has lunch with and is later takes an evening walk with is Mary Tyler Moore's then-husband Grant Tinker, president and co-founder of MTM. The woman who scowls at Mary as she tosses her hat is local resident Hazel Frederick.
Moore wore a wig for the first season of the show, to make her look less like Laura Petrie, her character on The Dick Van Dyke Show (1961). When the wig was discarded, the change in her hairstyle, including her much lighter hair color, was never commented on in the show itself.
The photo of Edward Asner playing football on Lou Grant's office wall is the same photo that was used in an episode of The Fugitive (1963) ('Three Cheers for Little Boy Blue') in which Asner guest starred.
In the opening credits, the shot of Mary Tyler Moore throwing her hat into the air was shot at the corner of 7th Street and Nicollet Mall in downtown Minneapolis. The buildings in the background were destroyed November 25, 1982, by a fire that took out a city block. Many scenes in the opening credits, including riding an escalator and window shopping, were shot within a one-block radius of the spot. In May 2002, TV Land erected a statue of her at that spot, facing the opposite direction.