Democrats also elected Dick Durbin of Illinois as assistant senate majority leader.
He had also been senate assistant minority leader since January last year.
Senate Republicans are to elect their leadership for the new congress on Wednesday, while the two parties select their leadership in the House on Thursday and Friday.
Reid was born in 1939, in the small desert town of Searchlight, Nevada.
He grew up in a shack with no toilet or hot water and his father was a miner who later committed suicide.
His mother did washing for local brothels to make ends meet.
Reid was a former amateur boxer who earned a law degree while working as a US Capitol policeman, Reid was first elected to the senate in 1986 after four years in the House of Representatives.
He is fond of saying: "I always would rather dance than fight, but I know how to fight."