He wrote the lyrics to the opening theme for the television show The Love Boat, with music previously composed by Charles Fox, which was originally sung by Jack Jones and, later, by Dionne Warwick.

Williams and Nichols were responsible for a number of successful pop hits from the 1970s, including several hits for Three Dog Night ("An Old Fashioned Love Song", "The Family of Man" and "Out in the Country"), Helen Reddy ("You and Me Against the World"), and the Carpenters, most notably "Rainy Days and Mondays", "I Won't Last a Day Without You", and "We've Only Just Begun", originally a song for a Crocker National Bank television commercial featuring newlyweds, and which has since become a cover-band standard and de rigueur for weddings throughout North America.

He contributed lyrics to the Cinderella Liberty song "You're So Nice to Be Around" with music by John Williams, and it earned them an Oscar nomination.

Along with Ascher and Rupert Holmes, he wrote the music and lyrics to A Star Is Born (also 1976), with Barbra Streisand and Kris Kristofferson.

[19] In March 2012, it was announced that Williams had "written a couple of tunes" on Random Access Memories, the album of French electronic duo Daft Punk.

Williams told an anecdote about his work with Daft Punk: "Back when I was drinking, I would imagine things that weren't there and I'd get frightened.

He communicated a "message from the robots" to the audience: "As elegant and as classy as the Grammy has ever been is the moment when we saw those wonderful marriages and 'Same Love' is fantastic.

In April 2009, Williams was elected president and chairman of the American Society of Composers, Authors and Publishers (ASCAP).

[23] In September 2015, Williams, along with bass player Kasim Sulton, led a global virtual songwriting collaboration at Hookist.com.

[24] The mission was to write the first crowd-sourced anthem to be performed at FacingAddiction.org's concert and rally on The National Mall on October 4, 2015, headlined by Steven Tyler, Sheryl Crow and Joe Walsh among others.

Williams, Sulton and Dr. Mehmet Oz opened the show and led 10,000 people in a singalong of "Voice of Change" at the base of the Washington Monument.

[27] Although predominantly known for his music, Williams has appeared in films and many television guest spots, such as the Faustian record producer Swan in Brian DePalma's film Phantom of the Paradise (1974)—a rock and roll adaptation of The Phantom of the Opera, Faust, and The Picture of Dorian Gray, for which Williams wrote the songs[28]—and as Virgil, the genius orangutan in Battle for the Planet of the Apes (1973).

[29] On February 9, 1973, Williams made a joke appearance on The Tonight Show Starring Johnny Carson in which he sang a song in full make-up as Virgil.

He has also appeared on Cartoon Network's Dexter's Laboratory[34] where he played Professor Williams[35] in an episode entitled "Just An Old Fashioned Lab Song".

He made numerous television appearances in the 1970s and 1980s, including on The Odd Couple, Hawaii Five-O, Match Game '79, Hollywood Squares, The Love Boat, Police Woman, Fantasy Island, The Hardy Boys, The Fall Guy, The Flip Wilson Special, Gimme a Break!, and The Gong Show.

He appears as the man making the phone call at the beginning of the music video for Hank Williams Jr.'s song "All My Rowdy Friends Are Coming Over Tonight".

[45] In September 2011, director Stephen Kessler's documentary Paul Williams Still Alive premiered at the Toronto International Film Festival.