His wife Michelle said he died at his home in Los Angeles.
Goffin, who married King in 1959 while they were in their teens, penned more than 50 top 40 hits, including Pleasant Valley Sunday for the Monkees, Some Kind Of Wonderful for The Drifters and Take Good Care Of My Baby by Bobby Vee.
He was able to pen jokey lyrics or achingly sad ones and also did it for solo artists and multiple voices.
Louise Goffin, one of his daughters, said her father "wore his heart on his sleeve and I am deeply blessed to have had a father who could so easily make the world laugh and cry with just a spiral notebook and a pen".
The couple divorced in 1968, but Goffin kept writing hits, including Savin' All My Love for You for Whitney Houston. Goffin and King were inducted into the Songwriters Hall of Fame in 1987 and the Rock and Roll Hall of Fame three years later.
King said Goffin was her "first love" and had a "profound impact" on her life.
"Gerry was a good man with a dynamic force, whose words and creative influence will resonate for generations to come," she said. "His words expressed what so many people were feeling but didn't know how to say."
The Goffin-King love affair is the subject of the Tony Award-nominated musical Beautiful: The Carole King Musical on Broadway. King, while backing the project, and with one of their daughters acting as a producer, had avoided seeing it for months because it dredged up sad memories. She finally sat through it in April.
The musical shows the two composing their songs at Aldon Music, the Brill Building publishing company in Manhattan that also employed Neil Sedaka, Howard Greenfield and Carole Bayer Sager.
The show ends just as King is enjoying fame for her groundbreaking solo album Tapestry. Though it also alleges Goffin's womanising and mental instability were causes of the break-up, he happily attended the opening of the musical.
After their divorce, Goffin garnered an Academy Award nomination with Michael Masser for the theme to the 1975 film Mahogany for Diana Ross. He also earned a Golden Globe nomination for So Sad The Song in 1977 from the film Pipe Dreams.
Goffin was born in Brooklyn in 1939 and was working as a chemist when he met King at Queens College.
"She was interested in writing rock 'n' roll, and I was interested in writing this Broadway play," Goffin told Vanity Fair in 2001.
"So we had an agreement where she would write (music) to the play if I would write (lyrics) to some of her rock 'n' roll melodies. And eventually it came to be a boy-and-girl relationship. Eventually I began to lose heart in my play, and we stuck to writing rock 'n' roll."
A whirlwind romance led to a marriage and their first hit, when she was only 17, Will You Love Me Tomorrow for the Shirelles, which a pregnant King helped write while suffering morning sickness.
Both quit their day jobs to focus on music, and other songs followed, including Up On The Roof for the Drifters, One Fine Day for the Chiffons and Chains, which was later covered by the Beatles. Goffin also collaborated with another Aldon composer, Barry Mann, on the hit Who Put The Bomp (In The Bomp Bomp Bomp Bomp).
King and Goffin wrote The Loco-Motion, which was eventually sung by their one-time babysitter Little Eva.
Goffin continued co-writing songs, including I've Got to Use My Imagination, recorded by Gladys Knight and the Pips, and It's Not the Spotlight, recorded by Rod Stewart. In the 1980s and 90s, he co-wrote Tonight I Celebrate My Love, a duet recorded by Peabo Bryson and Roberta Flack, Miss You Like Crazy, sung by Natalie Cole, and the Whitney Houston mega-hit Savin' All My Love for You.
"Gerry was one of the greatest lyricists of all time and my true soul brother. I was privileged to have had him in my personal and professional life," said pianist and composer Barry Goldberg, who wrote many later songs with Goffin.
Goffin is survived by his five children and his wife.