Through the years, musical theater has produced tightknit composing teams, with John Kander and Fred Ebb arguably leading the pack. But it’s a good wager that few of them were so tight that they went in on a washer-dryer together.

That’s what Laurence O’Keefe and Nell Benjamin, the composer-lyricists of the new Broadway musical “Legally Blonde,” recently did. Mr. O’Keefe and Ms. Benjamin are not only married to their work but to each other. “Legally Blonde” — based on the 2001 comedy starring Reese Witherspoon as a California ditz who turns Harvard Law on its ear — is their fifth collaboration and by far their biggest to date.

“We figured out we liked working with each other,” Mr. O’Keefe said. “We were rewriting each other’s stuff anyway. It was like a free service we were providing.” Their first collaboration dates back to their days at Harvard, where in 1993 they wrote the 145th edition of the notorious undergraduate show known as the Hasty Pudding Show. Mr. O’Keefe later found fame with the quirky musical fable “Bat Boy,” for which he wrote both music and lyrics. Since then, the two have largely operated as a double act, writing “Mice” (part of the Harold Prince-directed triptych of one-act musicals “3three”), “Sarah, Plain and Tall,” and “Cam Jansen.”

“Legally Blonde,” their Broadway debut, is also the first show of theirs to bear the clean and simple credit “music and lyrics by Laurence O’Keefe and Nell Benjamin.” In the past, Ms. Benjamin functioned primarily as a wordsmith, while Mr. O’Keefe was the music man. “When we get our own project and it’s just the two of us, I tend to lean a little more toward music and she tends to lean a little more towards book, and we duke it out on the lyrics,” Mr. O’Keefe said. “But on a show like this, when Heather Hach is the book writer, we’re just very meddlesome in each other’s music and lyrics.”

The couple auditioned for the “Legally Blonde” gig by sending in some sample songs intended for the show. Producer Hal Luftig sent a mixed tape of unidentified tunes to director-choreographer Jerry Mitchell, and Mitchell gravitated toward the couple’s work. A few of those songs are still in the show, including the opening tune “Omigod You Guys.”

That title — which succinctly sums up lead character Elle Woods’s pre-Harvard, girly-girl milieu — was Ms. Benjamin’s idea. “It seems to unlock” the song, remembered Mr. O’Keefe. The couple did some fieldwork at the Kappa Kappa Gamma sorority house at the University of Southern California — where Reese Witherspoon boned up on Greek campus life. “When we went to the sorority,” Ms. Benjamin recalled, “they asked if we had any songs. And I said we had one called ‘Omigod You Guys.’ And they said, ‘Omigod you guys, that’s great!’ Then ‘Omigod you guys, I said it!’ ‘Omigod, I said it again.'”

The composing team did not have to do any research to get a feel for the daunting world of Harvard, however. “On some levels, for both of us, Harvard was a little like an Elle Woods experience,” Mr. O’Keefe said, “because Elle goes to Harvard not realizing at all how completely out of place she is. We both came from relative comfort, but nonetheless, when you go to Harvard you realize there are all these levels of high-powered people, children and grandchildren of Nobel Prize winners. There’s this entire stratosphere of achievement and society that we never came near, and it’s very intimidating.”

Perhaps as intimidating as opening a show on Broadway, which they will do April 29. The date is easy for them to remember; it’s one day after their wedding anniversary.

“We’re going to celebrate our anniversary with a big party and a show,” joked Mr. O’Keefe.

“The next night,” Ms. Benjamin added.