The case involves Adam Clayton Powell Jr., an elected member of the House of Representatives who was excluded from taking his seat due to allegations of misconduct. Powell and his constituents filed a lawsuit claiming that the House could only exclude him if he did not meet the constitutional requirements, which he did meet. The Supreme Court agreed, finding that Powell was unlawfully excluded from the 90th Congress. The case also involves the Speech or Debate Clause, which protects not only words spoken in debate but also committee reports, resolutions, voting, and things generally done in a session of the House by one of its members in relation to the business before it. The Court ruled that Powell's claim for back salary is still valid, even though he has been seated in the 91st Congress. The Speech or Debate Clause does not provide complete immunity to legislators and does not prevent judicial review of legislative acts. House employees can be held responsible for unconstitutional actions. The Court concludes that the Constitution does not give the House the authority to exclude duly elected members who meet the requirements for membership expressly prescribed in the Constitution. The case is justiciable, and the court has subject matter jurisdiction.

The court examines historical precedents to determine the House of Representatives' power to judge the qualifications of its members. Congress cannot alter the qualifications for membership as a Representative contained in the Constitution. The court has jurisdiction over the subject matter of the controversy, and the claim is justiciable. Justice Stewart dissented, arguing that events since the case was granted certiorari have made it moot. The only remaining aspect of the case is Congressman Powell's individual claim for the salary he was deprived of during his absence from the 90th Congress. The Court lacks sufficient information to provide a remedy and must treat the case as moot without prejudice to a separate suit by the Senator.

Powell is suing the Sergeant at Arms of the House for salary, but it's unclear if there's a remedy. Powell can seek a money judgment against the US in the Court of Claims. The court should dismiss Powell's case against the legislative branch to avoid constitutional issues. The court should determine if there's effective relief before deciding the case. Powell has a better remedy for back-pay, and the case against all respondents is moot, so the court should dismiss the complaint. The lower court didn't address the remedy question.