Jerry Lawson, who for four decades was the lead singer of the Persuasions, a group that revived the art of a cappella singing and attracted a loyal worldwide following, died on Wednesday in Phoenix. He was 75.

His death was confirmed by his wife, Julie. She said that Guillain-Barre syndrome, a rare neurological disorder, had compromised Mr. Lawson’s immune system.

Led by Mr. Lawson’s smooth, warm baritone, the Persuasions sang R&B, rock, blues, gospel and pop with no instrumental accompaniment, long after the doo-wop era that their sound evoked and long before the recent “Pitch Perfect” movies brought new attention to a cappella singing.