In a Songfacts interview with Paul Williams
, he told the story behind this song: "'It had all the romantic beginnings of a bank commercial' is the way I describe it. There was actually a wonderful writer named Tony Asher who wrote for this ad agency, and he'd had a skiing accident and he broke his arm, so he couldn't write or play the piano or whatever. So he suggested Roger Nichols and I as replacements to write this ad. The ad agency called us and said, "Look, we're going to show a young couple getting married, driving off into the sunset, and it's going to say, 'You've got a long way to go, we'd like to help you get there to the Crocker Bank.'" And I went, Okay, what rhymes with Crocker? Crocker what? And they said very specifically, "No we don't want a jingle." What they asked for is what we would today call a music video. It was going to show a young couple getting married, driving off into the sunset. After the ceremony, the first kiss and all. So Roger and I wrote the song that would play over that.
We wrote the first two verses of 'We've Only Just Begun.' We wrote a second version of the commercial that was a verse, and what became the bridge. We added a third verse just in case anybody would ever want to record it. And then I assumed that it would never, ever get cut again. Richard (Carpenter), I guess, heard me singing it on the TV commercial, and called and asked if there was a complete song. And we went, 'Well, funny you should ask.' And if there hadn't been a complete song, we would have lied and said, 'Well, of course there is,' and then sat down and written it. You know, songwriting in those days was like that, too. I remember finishing songs in the back seat of a publisher's car on the way to play it for a producer. I retained my rights as a writer, and the publisher retained his rights as well."