Born in Rochester, New York, Larimer received a B.A. from St. John Fisher College in 1966 and a J.D. from Notre Dame Law School in 1969. He served as a law clerk for Hon. Joseph C. McGarraghy, U.S. District Court, District of Columbia from 1969 to 1970. After this, he was an assistant U.S. Attorney of the Washington, D.C. from 1970 to 1973. In the following years, Larimer worked as an assistant U.S. Attorney of the Rochester, New York from 1973 to 1975. He was in private practice in Rochester, New York from 1975 to 1979. An Adjunct instructor of law, David G. Larimer taught at St. John Fisher College from 1978 to 1981. He was a Chief appellant law assistant, Supreme Court, Appellate Division Fourth Department, Rochester, New York from 1979 to 1981. He was in private practice in Rochester, New York from 1982 to 1987.