"Mayor Booker is a results oriented leader who will bring the type of common sense leadership to the U.S. Senate that Washington needs right now," O’Malley said according to the New Jersey Star-Ledger. "Over the past seven years, Mayor Booker has worked tirelessly to improve Newark’s schools, reduce violent crime, spur economic growth, expand opportunity and create jobs."

O'Malley's endorsement comes just a few days after Booker formally jumped into the race for deceased Sen. Frank Lautenberg's (D-N.J.) Senate seat.

O'Malley is likely to campaign for Booker in New Jersey in the next months, ahead of the August primary, according to the Star-Ledger.

The Maryland governor's endorsement is likely to help Booker with fundraising as O'Malley is a high profile Democrat often mentioned as a possible 2016 presidential candidate.

Booker, in the past, has said he expects O'Malley to face former Secretary of State Hillary ClintonHillary Diane Rodham ClintonColorado governor teases possible presidential run Mueller asks judge for September sentencing for Papadopoulos House Judiciary Committee subpoenas FBI agent who sent anti-Trump texts MORE in the 2016 Democratic primary.

"It'll be him versus Hillary," Booker said, according to Buzzfeed.

Rep. Frank Pallone (D-N.J.) also recently jumped into the race for Lautenberg's Senate seat.