Mr. Harper, who was 62, had entered a Manhattan hospital in recent days. The cause of death was apparently cardiac arrest. He had been in poor health for several years.
Mr. Harper was seen and heard most recently in Barbara Cook's Broadway, her concert of theatre songs at Lincoln Center Theater and on tour. He was musical director and handled arrangements for the lauded show, in which Cook shares anecdotes about her life in the theatre. Their work is preserved on a live-audience cast album on the DRG label. That record company also recorded many of Mr. Harper's cabaret and concert shows with Cook over the past 30 years.
Mr. Harper was a graduate of the New England Conservatory and the Juilliard School of Music and worked in various musical capacities on such Broadway shows as Billy, Company, Irene, Peter Pan (the 1979 revival), The Grand Tour, Brigadoon (the 1980 revival), Nine, A Day in Hollywood/A Night in the Ukraine, Grand Hotel, My One and Only and The Best Little Whorehouse in Texas.
His job titles on Broadway included dance arranger, vocal arranger, pianist, conductor, songwriter and composer of incidental music.
Mr. Harper composed the Off-Broadway musical, Sensations, and several songs for the Broadway revival of Irene starring Debbie Reynolds. In the summer of 2001, the premiere of Say Yes!, with music by Wally Harper and book and lyrics by Sherman Yellen, was presented at the Berkshire Theatre Festival in Stockbridge, MA. Jay Binder directed. The musical was "a romantic love story set against the background of the 1939-1940 New York World's Fair," according to BarbaraCook.com.
Mr. Harper produced the cast albums of My One and Only, A Day in Hollywood and the Pointer Sisters in Ain't Misbehavin', as well as Tommy Tune's Slow Dancin'.
Mr. Harper conducted symphonies around the world and performed in the White House for four administrations.
Cook and Mr. Harper were one of the successful professional marriages in show business. Together, they created intimate piano-and-voice shows for boites and more lavish orchestral concerts for venues such as Carnegie Hall.
In 2002, when they were presenting a concert called Mostly Sondheim, inspired by a published list of songs Stephen Sondheim wished he'd written, Cook spoke to Playbill On-Line about how she and Mr. Harper created shows. Answering the question "How much suggesting does Wally do and how much do you do?," she said, "There's no way to quantify that. We do it together. In this case, we needed to find something, a show with a theme that would allow us to do songs that we felt we knew, because we didn't have very much time to work on this act. As it turns out, I had 11 new songs [to learn]! This is not at all what our original intent was — we needed something that would be kind of easy on us. I suggested we do songs from shows that I wished I had been in, or something like that. For some reason, suddenly Wally said, 'Wait a minute, why don't we do a show along the lines of that list that Stephen had written and then do some Stephen Sondheim...' We were already kind of committed to it before we realized, My God, this is gonna take a lot of work!"
Earlier this year, she told Playbill On-Line, "We met a long time ago, but I remember meeting him in 1973 and we started working together. I was doing a concert tour of Gershwin songs with several other people, and [Wally] visited us a couple of times."
In his career with Cook, Mr. Harper arranged and conducted the CD "Oscar Winners: The Lyrics of Oscar Hammerstein II," and produced and arranged "It's Better With a Band," for which he wrote the title song with David Zippel, and "The Disney Album," arranged for symphony orchestra. He co-produced "Close as Pages in a Book," a Cook disc of songs by Dorothy Fields; "Barbara Cook Live from London," "Barbara Cook at Carnegie Hall," "As of Today," "All I Ask of You," "The Champion Season" and "Barbara Cook Sings Mostly Sondheim."
His most recent album with Barbara Cook was "Count Your Blessings," which he co-produced and conducted.