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

Mr. Ashford had throat cancer and was undergoing treatment at a New York hospital, but the cause of his death was not immediately reported. His death was announced by the music publicist Liz Rosenberg.

One of Motown’s leading songwriting and producing teams, 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,” while also making cuter promises like “If you’re ever in trouble, I’ll be there on the double.” Gaye and Terrell also sang the duo’s songs “Your Precious Love,” “Ain’t Nothing Like the Real Thing” and “You’re All I Need to Get By.” After leaving the Supremes in 1970, Diana Ross sang their “Reach Out and Touch Somebody’s Hand,” and later that year her version of “Ain’t No Mountain High Enough” became her first No. 1 single as a solo artist.

“They had magic, and that’s what creates those wonderful hits, that magic,” Verdine White of Earth, Wind and Fire told The Associated Press after learning of his friend’s death. “Without those songs, those artists wouldn’t have been able to go to the next level.”