President Obama and Elizabeth Warren in her new ad.

Elizabeth Warren is bringing out the big guns in her race against Scott Brown. A new ad for the Massachusetts Senate hopeful features President Barack Obama touting her as a champion of the middle class.

"She's a janitor's daughter who has become one of the country's fiercest advocates to the middle class," President Obama said in the ad. 

Ms. Warren is fighting a close race against freshman Republican Scott Brown. Her new ad focuses on her work advising the White House on the establishment of the new Consumer Financial Protection Bureau watchdog agency.

"She came up with an idea for a new, independent agency that would have one simple, overriding mission--standing up for consumers and middle class families," President Obama said.

The Massachusetts race is one of the most closely watched and tightly contested races this year. It has also proven to be the costliest Senate contest of this election cycle with more than $30 million in donations going to both candidates. Ms. Warren's campaign has beneffitted from a large number of contributions from outside Massachusetts.

Watch Ms. Warren's new ad below.