While at Alabama, Cohn was a member of the Zeta Beta Tau fraternity.
He served as assistant public defender in the Broward County, Florida, Public Defender's Office in 1975 and as assistant state attorney in the Broward County State Attorney's Office in 1975 to 1978.
He was in private practice in Fort Lauderdale from 1978 to 1995; he worked for a year with the Michael Widoff law firm before beginning his own general trial practice in 1979.
President George W. Bush nominated Cohn on May 1, 2003 to the United States District Court for the Southern District of Florida, to the new seat created by 116 Stat.
He was confirmed by the Senate on July 31, 2003, and he received his commission on August 1, 2003.