Maggie Roche, the songwriter whose serene alto anchored the close harmonies of the Roches, her trio with her sisters, Terre and Suzzy, died on Saturday. She was 65.

Suzzy Roche said in a statement that the cause was breast cancer. She did not say where her sister died.

“She was a private person, too sensitive and shy for this world, but brimming with life, love, and talent,” Suzzy Roche wrote on the Roches’ Facebook page. “She was smart, wickedly funny, and authentic — not a false bone in her body — a brilliant songwriter, with a distinct unique perspective, all heart and soul.”

Ms. Roche developed a pop-folk songwriting style that could be droll or diaristic, full of unexpected melodic turns and often inseparable from the way the sisters’ voices harmonized and diverged...