Senator Robert Menendez of New Jersey has been charged in a federal corruption indictment, the authorities said on Friday.

The indictment against Mr. Menendez, a 69-year-old Democrat who leads the Senate’s Foreign Relations Committee, follows a lengthy investigation by federal prosecutors in Manhattan and comes nearly six years after his trial on unrelated claims of corruption ended with a hung jury.

It has been known for some time that Mr. Menendez was under federal scrutiny, and he has said he was willing to assist investigators and was confident the matter would be “successfully closed.”

Representatives for Mr. Menendez could not immediately be reached for comment on the charges.

The indictment is almost certain to resound in Washington and in New Jersey.

Mr. Menendez is already facing at least one Democratic challenger in his planned run for re-election to a fourth term in the Senate, and the Republican mayor of Mendham Borough, N.J., has also announced that she will compete for the seat.

If Mr. Menendez were to step down before the end of his term, New Jersey’s Democratic governor, Philip D. Murphy, would be responsible for appointing a successor.

This is a developing story and will be updated.

Kirsten Noyes contributed research.