The apportionment of seats in this House of Representatives was based on the 1960 United States census, and the number of members was again 435 (it had temporarily been 437 in order to seat one member each from recently admitted states of Alaska and Hawaii).

Both chambers maintained a Democratic majority - including a filibuster-proof supermajority in the Senate - and with President Kennedy, the Democrats maintained an overall federal government trifecta.

Senators are popularly elected statewide 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 1 meant their term ended with this Congress, requiring reelection in 1964; Class 2 meant their term began in the last Congress, requiring reelection in 1966; and Class 3 meant their term began in this Congress, requiring reelection in 1968.

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.