The apportionment of seats in the House of Representatives was based on the 1910 United States census.

With Woodrow Wilson being sworn in as president on March 4, 1913, this gave the Democrats an overall federal government trifecta - also for the first time since the 53rd Congress.

Most senators were elected by the state legislatures every two years, with one-third beginning new six-year terms with each Congress.

Preceding the names in the list below are Senate class numbers, which indicate the cycle of their election, In this Congress, Class 3 meant their term ended with this Congress, requiring reelection in 1914; Class 1 meant their term began in the last Congress, requiring reelection in 1916; and Class 2 meant their term began in this Congress, requiring reelection in 1918.

The directory after the pages of terms of service lists committees of the Senate, House (Standing with Subcommittees, Select and Special) and Joint and, after that, House/Senate committee assignments.