He was born in Minneapolis, Minnesota. McGregor was a delegate to the Republican National Convention from Minnesota in 1964 and 1968. He was an unsuccessful candidate for U.S. Senator from Minnesota in 1970. McGregor was Assistant to Richard Nixon for Congressional relations in 1970, Counsel to the President on Congressional Relations (1971 - 1972), Chairman of the Committee to Re-elect the President (July to November 1972) following John Mitchell's resignation from the position in the Watergate political scandal.