He won the NYSAC World Light Heavyweight Title by beating Lou Scozza on February 10, 1930 in Broadway Auditorium. Slattery lost the title later that year in a bout at Bison Stadium against Maxie Rosenbloom for the NYSAC World Light Heavyweight Title and the Undisputed World Light Heavyweight Title. The verdict was "highly unpopular" with the 15,000 fans at the fight.
Slattery's victory over Lou Scozza in February 1930 marked his rise as champion of the NYSAC World Light Heavyweight division. However, his subsequent loss to Maxie Rosenbloom at Bison Stadium later that year for both titles was met with widespread disapproval from the crowd of 15,000 fans.