Speaking on Late Night With Jimmy Fallon, McCartney revealed that the pair had "got [their] friendship back together" after having "a lot of business problems".
He made the comments in the wake of the 30th anniversary of Lennon's murder by Mark Chapman, which was marked by his family, friends and fans around the world on December 8.
"We'd chat about how to make bread. Just ordinary stuff, you know. He'd had a baby by then - he'd had Sean - so we could talk babies and family and bread and stuff. So that made it a little bit easier, the fact that we were buddies," McCartney said.
He also spoke out about Lennon's "senseless" murder, adding: "A phrase kept going in my head about the guy who killed him: Jerk of all jerks. It was just so, so sad because we thought John would be around forever, we'd hang."
The singer, who is due to play two Christmas gigs in London and Liverpool later this month, also performed 'Here Today' on the US chatshow as a tribute to Lennon.
Earlier this week, Lennon's widow Yoko Ono told NME that he would "definitely be experimenting on some new music" were he still alive today.
This week's issue of NME, which is on UK newstands and is available digitally worldwide, also features an interview with Sean Lennon, as well as features on John Lennon's life and his final days.
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