He served as chairman of the Committee on Expenditures in the Department of War (Twenty-third Congress) before resuming the practice of law.
Whittlesey served as the City Attorney of Rochester in 1838 and as vice chancellor of the eighth judicial district of New York from 1839 to 1847.
He became justice of the State supreme court in 1847 and 1848 and then a professor of law at Genesee College (now Syracuse University) in 1850 and 1851.
He died of typhus fever in Rochester, New York, September 19, 1851 and was interred in Mount Hope Cemetery.
[1] This article incorporates public domain material from the Biographical Directory of the United States Congress