Professor O'Bryant's current research is in additive number theory. A general notion in this area is that if a sumset is extremely small, or extremely large, then the underlying set should have some rough structure. This field draws on probability theory, graph theory, logic, ergodic theory, and combinatorics, and has been serving as a mathematical honeybee for these areas, carrying ideas and progress from each area to the others. Prof O'Bryant earned his Ph. D. at the University of Illinois at Urbana-Champaign in 2002, and came to CUNY after 3 years as an NSF postdoc at the University of California, San Diego. His bachelor's degree, from the Rose-Hulman Institute of Technology, was in Applied Mathematics.

He is also on the faculty of CUNY's Graduate Center, and speaks frequently in the New York Number Theory Seminar. He is a co-organizer of the Combinatorial and Additive Number Theory Conference, held yearly in May in New York City.