Slattery, son of a Buffalo fire fighter, turned pro in 1921 and came up short in his challenge for the World Light Heavyweight Title against Paul Berlenbach in 1925.

Slattery won the vacant NBA light heavyweight title in August 1927 with a decision over Maxie Rosenbloom, only to lose it to Tommy Loughran in December of that year.

He won the NYSAC World Light Heavyweight Title by beating Lou Scozza on February 10, 1930, in Broadway Auditorium.

Referee Patsy Haley, after being almost knocked out by one of Rosenbloom's wild swings, gave his decision to Slattery.

[2] During the Great Depression, Slattery was known to throw money out of the window of his car while driving through the streets in order to help the poor children buy new shoes for school.