He was in private practice in Washington, D.C. from 1940 to 1942, and was then in the United States Army Air Forces during World War II, from 1942 to 1945, returning to private practice in Washington, D.C. from 1945 to 1948.
He again returned to private practice in Washington, D.C. from 1962 to 1969, and was the United States Attorney for the District of Columbia from 1969 to 1971.
[1] On November 18, 1971, Flannery was nominated by President Richard Nixon to a seat on the United States District Court for the District of Columbia vacated by Judge Leonard Patrick Walsh.
He assumed senior status on May 10, 1985, serving in that capacity until his death on September 20, 2007, in Washington, D.C.[1] Since 2009 the D.C. Bar has sponsored an annual Thomas A. Flannery lecture.
Speakers have included Supreme Court justices Antonin Scalia and Ruth Bader Ginsburg.