The show was originally planned to be about a divorced woman, but because divorce was still a hot subject in 1970, they settled for a broken engagement instead. Also, the network was afraid people would think that Mary had divorced Rob Petrie, her character's husband on The Dick Van Dyke Show (1961), losing the audience's sympathy.
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).
The two joggers who pass Mary in the park during the opening credit sequence are producers James L. Brooks and Allan Burns. Also in the credit sequence, the gray-haired man Mary has lunch with and is later seen walking with in the evening is Mary Tyler Moore's then-husband Grant Tinker, the president/co-founder of MTM. The woman seen scowling back 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 appear less like Laura Petrie (her character on The Dick Van Dyke Show (1961).) When it 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.
The shot in the opening credits where Mary Tyler Moore throws her hat into the air was shot at the corner of 7th Street and Nicollet Mall in downtown Minneapolis. In May 2002, TV Land erected a statue of her at that spot. The statue faces the opposite direction, however: the buildings that appear in the background of the shot were destroyed by a fire that took out an entire city block on Thanksgiving night in 1982. Many scenes in the opening credits (riding an escalator, window shopping) were shot within a one-block radius of this spot.
The kitten who meows at the end of the closing credits is a parody of the roaring lion which appears at the beginning of MGM films. The kitten's name was "Mimsey"; she was adopted from a local shelter.