Robert Santelli's The Big Book of the Blues ran through the standard biography, but the sort of detail I was looking for finally arrived in Rick Koster's Louisiana Music.
The rest of the sources deliver much the same story. New Orleans born Dorsey lived in the same Ninth Ward neighbourhood as Fats Domino until his family moved to Oregon when he was ten. After wartime service in the Navy (Koster: the Marines) and a career as a lightweight boxer (Mr. TNT, Cadillac Shorty, Kid Chocolate) he was back in New Orleans in 1955, working as a mechanic. He sang while he worked, which brought him to the attention of independent record producer Reynauld Richard when the latter called in to collect his car.
That was the genesis of Lottie Mo, recorded for the Valiant label in 1958 and picked up by ABC Paramount in 1961. That, in turn, brought him into contact with Toussaint's colleague Marshall Sehorn, who liked the song, tracked the singer down to his Ninth Ward home. Dorsey was light on for new material but with Sehorn, over a couple of brews, he reworked a neighbourhood kids' chant about a constipated mother into Ya Ya. The song went to number seven on the Billboard charts in 1961, moved a million copies, and the rest, as they say, is history.
Or, perhaps, not quite. Dorsey kept working New Orleans clubs and cutting records through that string of significant hits in the US and UK charts and toured internationally. Then, when things started to run out of puff, he headed back to the auto repair business.
There were revivals thanks to Southside Johnny and the Asbury Jukes and The Clash (he and Joe Ely opened on their 1980 US concert tour), James Brown and Jerry Lee Lewis. A 1979 hit and run accident broke both his legs and confined him to a wheelchair for a while, but he bounced back until a lengthy bout of emphysema.