Booker, now in his second term as mayor of Newark, defeated three rivals in the Democratic primary last week.
"Cory Booker has dedicated his life to the work of building hope and opportunity in communities where too little of either existed," Obama said in a statement released by the Booker campaign. "Whether as a college student working in East Palo Alto or as mayor of New Jersey's largest city, Cory has time and again taken on tough challenges, fought for the middle class and those working to join it, and forged coalitions that create progress -- and that's the spirit he'll carry with him to Washington.
Obama and Booker have much in common. Booker, the son of two of IBM's first black executives, grew up in a mostly white New Jersey suburb, went to Stanford and attended Oxford as a Rhodes scholar.
Booker moved to Newark after receiving a law degree from Yale. He served on the city council before becoming mayor in 2006.
While Booker backed Obama in 2008 and 2012, he also criticized him for attacking private equity.
Booker is favored to defeat Republican Steve Lonergan in the October election being held to fill the seat left vacant by the death of Frank Lautenberg. If he wins, he will be New Jersey's first black senator.
New Jersey has not elected a Republican to the Senate since 1972.