Nick Ashford, who with Valerie Simpson, his songwriting partner and later wife, wrote some of Motown’s biggest hits, like “Ain’t No Mountain High Enough“ and “Ain’t Nothing Like the Real Thing,” and later recorded their own hits and toured as a duo, died Monday at a hospital in New York City. He was 70 and lived in Manhattan.

Mr. Ashford had throat cancer and was undergoing treatment, but the cause of his death was not immediately known. His death was announced by Liz Rosenberg, a friend who is a longtime music publicist.

One of the primary songwriting and producing teams of Motown, Ashford & Simpson specialized in romantic duets of the most dramatic kind, professing the power of true love and the comforts of sweet talk. In “Ain’t No Mountain High Enough,” from 1967, their first of several hits for Marvin Gaye and Tammi Terrell, lovers in close harmony proclaim their determination that “no wind, no rain, no winter’s cold, can stop me, baby,” but also make cuter promises: “If you’re ever in trouble, I’ll be there on the double.”...