The governor, considered a likely 2016 presidential contender, sent out a tweet on Tuesday alerting his followers to his plans.
"Excited to join @corybooker on the campaign trail in New Jersey this Thursday," he tweeted.
According to PolitickerNJ, O'Malley will make stops on his own in Trenton and Paterson and appear with Booker in Newark, N.J.
He's previously helped another New Jersey Democrat, gubernatorial candidate Barbara Buono, to raise cash, lending his name to a fundraising email sent out by her campaign last month.
Booker remains the front-runner in the New Jersey special Senate election, and will likely nab the Democratic nomination in next week's primary. Democrats are expected to win the seat in the general.
O'Malley has begun to dip a toe into 2014 campaigns elsewhere, contributing through his O’ Say Can You See PAC to Iowa Rep. Bruce BraleyBruce BraleyTrump: Ernst wanted 'more seasoning' before entertaining VP offer Criminal sentencing bill tests McConnell-Grassley relationship Trump's VP list shrinks MORE (D), who's running for Senate there, and New Hampshire Sen. Jeanne Shaheen Jeanne ShaheenDems push for panel to probe Russian interference in election Hoyer pushes White House for briefing on Russian election interference This Week in Cybersecurity: Dems press for information on Russian hacks MORE (D), up for reelection next year. His dabbles in campaigns in early primary states have fueled rumors that he's preparing a presidential bid.
Booker, too, is considered a potential 2016 presidential or vice presidential contender, though he said recently he has no plans to run on a presidential ticket and is instead focused on the upcoming special.