A collaboration between former Walkmen lead singer Hamilton Leithauser and former Vampire Weekend multi-instrumentalist Rostam Batmanglij seems like something that should have happened long ago.

They both were key players in the New York alt-rock boom of the ’00s, and Vampire Weekend opened for the Walkmen early in their career. Yet the two of them weren’t close until Batmanglij suggested they try working together.

Two songs from those sessions wound up on Leithauser’s solo album, 2014’s “Black Hours,” and paved the way for their debut as a duo, “I Had a Dream That You Were Mine.” The album takes the classic songcraft of ’50s and ’60s pop, rock and soul, and gives it a modern twist.

amNewYork spoke with Leithauser.

What drew you to Rostam’s musical style?

I always liked [Vampire Weekend]. I rooted for them. ... I wanted to see what he could do, but I didn’t have a lot of faith it would work out. My music was different, and I didn’t know what his role would be when we got together.

So, it just developed naturally?

Yeah, it did. We have a similar aesthetic and we have a similar background. We’re both from Washington, D.C. We can refer to the same sort of obscure records we both like. That’s how you can build the trust you need when you’re working with a new person.

On this tour, you’ve performed with and without Rostam. Is it challenging to go back and forth?

I have a really great band. They can handle anything. Rostam just came out and did the shows in LA with me. He’ll be back a bunch actually, in and out for a long time, probably as long as I keep [the tour] going.

How do the songs change when you play them live?

Before our first show, we had a few band practices and realized we had never played the songs live. We wrote and recorded them simultaneously because we did it all at Rostam’s house in LA. I’d play some guitar lines, he’d edit them, we’d add drums in. We were doing it all in a piecemeal way. Then the record’s done and you’ve literally never played the songs. ... It took a lot to translate it into something that was possible [to play live].

What’s the status of The Walkmen?

We don’t have any plans right now. I wouldn’t rule it out. We have all this history. I think we’d have to have the desire to go out and play our back catalog as well as have a new record. That’s a big hill to climb right now.