Onorato Timothy O'Meara (born January 29, 1928) is an American mathematician known for his work in number theory, linear groups and quadratic forms. He is provost emeritus and professor emeritus of mathematics at the University of Notre Dame.

O’Meara is the author of Symplectic Groups, Introduction to Quadratic Forms, and The Classical Groups and K-Theory (co-author, Alexander J. Hahn[de]).

In 2008, the University of Notre Dame Mathematics Library was rededicated and named in his honor - the website is [1]