Clips from Casablanca (1943, see entry), Susan Lennox (Her Fall and Rise) (1931, see entry), and Father of the Bride (1950, see entry) appear within the film.
       The Happy Ending was announced as an upcoming United Artists (UA) production in the 2 Oct 1968 DV, which stated that Jean Simmons would star and her then husband, Richard Brooks, would write and direct. It marked the second time Simmons had worked with Brooks after Elmer Gantry (1960, see entry). Brooks reportedly maintained secrecy over the script throughout shooting and post-production, even with his wife, to keep “the same element of excitement and surprise with the actors as for the audience,” as noted in the 27 Jan 1969 DV. All cast members were said to have agreed to work on the project without seeing a script, and were availed of dialogue pages only forty-eight hours before scenes were scheduled to be shot.
       Principal photography began in Denver, CO, on 15 Jan 1969, as announced two days later in a DV production chart. The 5 Feb 1969 Var stated that the picture was “believed to be the first feature motion picture to have its locale and major production in Denver.” An article in the 22 Apr 1969 DV detailed that sixty percent of the film would be shot in Denver, while twenty-percent would be shot in Beverly Hills, CA, and fifteen-percent would be filmed in Nassau, Bahamas. Two days of shooting were also scheduled to take place at the Miami International Airport in Miami, FL. Locations in Denver included an abandoned May-Daniels & Fisher department store in the downtown area, and a general hospital, as noted in the 24 Jan 1969 DV and 6 Mar 1969 LAT. In Beverly Hills, a Coldwater Canyon residence that was used for interiors was rented for $1,500 per month.
       Gena Rowlands, who had initially been cast in the role of “Flo,” was replaced by Shirley Jones midway through production, the 2 Apr 1969 Var reported. No reason was given for Rowlands’s departure.
       Filming was completed thirty-two days ahead of the 106-day schedule, according to the 22 Apr 1969 DV, which noted the same forty-person crew had worked on Brooks’s two previous pictures, The Professionals (1966, see entry) and In Cold Blood (1967, see entry). Time-saving techniques included an umbrella lighting system devised by chief electric Harry Sundby, and the use of Nagra sound cameras which eliminated the need for a recording truck. Brooks estimated the time savings reduced the $2 million budget by $320,000. An estimate in the 8 Dec 1969 DV put the final cost of the film at $1.8 million.
       The 9 Oct 1969 DV noted that Michael Dees was set to record the title song, “What Are You Doing The Rest Of Your Life?” UA Records planned to release a single recorded by Dees, and the song was also slated to be recorded by Jaye P. Morgan for Beverly Hills Records, according to the 14 Jan 1970 DV.
       The film received an M-rating (suggested for mature audiences) from the Motion Picture Association of America (MPAA), as announced in a 12 Nov 1969 Var item. The following month, a 3 Dec 1969 Var brief stated that The Happy Ending would be shown for one week in late Dec 1969 in Los Angeles, CA, to qualify for Academy Award consideration. Academy Award nominations ultimately went to Jean Simmons for Best Actress, and to Michel Legrand, Alan Bergman, and Marilyn Bergman for Music (Song--Original for the Picture) for “What Are You Doing The Rest Of Your Life?” The Happy Ending received Golden Globe Award nominations for Best Original Score – Motion Picture, Best Performance by an Actress in a Motion Picture – Drama (Jean Simmons), and Best Original Song – Motion Picture (“What Are You Doing The Rest Of Your Life?”).
       After nearly a year in release, the 28 Oct 1970 Var indicated the film was one of several UA releases “having trouble” at the box office.
       Carol Ann Jackson was named as the second assistant film editor in a 27 May 1969 DV brief, and Jane Ruddick of the Illinois Talent agency in Denver, CO, claimed to have worked on the film in a 17 Dec 1969 DV advertisement.