PORTLAND — UNUM Corp. said Friday that former Sen. George J. Mitchell had been named to its board of directors.

Since retiring from the U.S. Senate last year, the former majority leader has joined a Washington law firm and the boards of Federal Express and the Walt Disney Co. Mitchell, 61, has also agreed to lecture at some Florida colleges.

“George Mitchell’s breadth of experience, reputation and knowledge of our company will make a valuable addition to our board,” said James F. Orr III, chairman of UNUM. “His national and international perspective will be particularly beneficial to our quest for worldwide leadership in disability and special risk markets.”

UNUM is a Portland-based insurance-holding company. Its assets totaled $13.1 billion at the end of 1994.