"Today, I ask for your support as I seek to serve as your Senator in that seat. The reason is simple: I believe I am the best candidate to continue the passionate advocacy for progressive values that Sen. Lautenberg exemplified," he said in a statement.

Multiple sources had previously confirmed Holt's intentions to run, but he's the first candidate to make his plans official. He's likely to face Newark Mayor Cory Booker, who is collecting signatures to run, and Rep. Frank Pallone in a Democratic primary.

The candidates are required to file 1,000 signatures on Monday to be added to the primary ballot, and with just five days to go, the scramble is on.

Lautenberg passed away early Monday morning, and New Jersey Gov. Chris Christie announced Tuesday the special election primary will take place Aug. 13, while the general election will occur Oct. 16.

Holt has long been contemplating a run for Senate, but the timing of the special improves his chances at the seat. Booker, however, remains the frontrunner in the race.