McGarraghy was born in Washington, D.C., and graduated from the Business High School. McGarraghy was in the engineering corps of the United States Army from 1917 to 1920 where he became an Army Field Clerk in 1918 and secretary in 1920.[1][2] He received a Bachelor of Laws from Georgetown Law in 1921. He was an assistant corporation counsel from 1924 to 1925. He was in private practice in Washington, D.C., from 1925 to 1954. He was President of the Washington Board of Trade from 1946 to 1947. He was Chairman of the Greater National Capital Committee from 1947 to 1950. He was a Chairman of the Republican State Committee in Washington, D.C., from 1949 to 1954. He was Chairman of the Eisenhower-Nixon Inaugural Committee in 1953.[3]