Born in Washington, D.C., he attended the public schools, Gonzaga College High School and Georgetown University. He was a clerk in the quartermaster's department during the Civil War. He moved to Dakota Territory in 1879 and settled in Larimore; he was interested in mail contracts for several years and was a member of the Territorial House of Representatives in 1885.

Roach was an unsuccessful Democratic candidate for governor at the first State election in 1889 and again in 1891. He was elected to the U.S. Senate and served from March 4, 1893, to March 4, 1899. In 1893, a subcommittee in the Senate was convened to hear evidence that Roach had embezzled money while acting as an officer of a bank. Expulsion was considered, but the subcommittee decided the matter was too long past to take such action.^[1] He was an unsuccessful candidate for reelection and discontinued active business pursuits and lived in retirement in Washington, D.C. He died in New York City on September 7, 1902; interment was in the Congressional Cemetery, Washington, D.C.

• List of United States senators expelled or censured

• United States Congress. "William N. Roach (id: R000290)". Biographical Directory of the United States Congress. Retrieved October 19, 2008.