Updated 10/31/2013 at 11:35 a.m.
Washington (CNN) - He didn't get sworn into the U.S. Senate until Thursday afternoon, but Cory Booker's nameplate was already up hours earlier outside his new office in the Senate Hart office building.
Earlier this month, the two-term Democratic Mayor of Newark, New Jersey, won a special election to serve out the final 14 and a half months of the term of the late Democratic Sen. Frank Lautenberg, who died in June.
Booker was sworn into the Senate by Vice President Joe Biden. Later in the day Booker heads to the White House for a meeting with President Barack Obama.
Soon after Lautenberg's death, New Jersey Gov. Chris Christie named fellow Republican and state Attorney General Jeff Chiesa to temporarily fill the Senate seat. That move reduced the Democratic Party's control of the Senate to 54-46. Booker's entry into the Senate brings the Democrats' majority back to 55-45.
Booker is considered a rising star in the Democratic Party. He's made national headlines in recent years for rescuing a neighbor from a fire and for helping his city dig out from a major snowstorm. But his near celebrity status also opened him to attacks by his critics that he spent far too much time outside of Newark, and that he didnt do enough to stem the city's rising murder rate.
–CNN's Paul Courson contributed to this report.