"I'm going to try to bring the same creativity and innovation that I brought to the mayor's job now to the U.S. Senate," Booker, 44, said at a news conference.
Later, speaking to reporters from regional media, he detailed some of his ideas. Booker cited a Newark police program that helps seize illegally owned guns by giving anonymous tipsters codes to claim $1,000 rewards from ATMs - if their information pans out - free tax centers to help poor residents claim income tax credits, and programs to help small businesses get access to capital.
"Why don't we have them in Camden?" he asked of the gun program. "Why don't we have one in Irvington? Why don't we have one in Paterson and Passaic?"
Booker, hoarse from the day's events, said he would crisscross the state to spread his vision beyond Newark.
"A lot of what people are going to see in my first six months is me going to places where they haven't had those kind of partnerships with an official that could help convene people, bring them together to get things done," Booker said in his new office - the walls almost entirely bare, desks empty, and carpets freshly cleaned.
Booker, above all, stressed economic concerns.
"Everybody I talk to, from Cumberland County to Bergen County, people are talking about economic issues," he said, citing foreclosures, New Jersey's "too high" unemployment rate, and poverty.
Long touted as a rising political star, Booker formally stepped into the national debate in a ceremony steeped in symbolism.
Among those who watched were U.S. Rep. John Lewis (D., Ga.), a civil rights icon, and Bonnie Englebardt Lautenberg, widow of Sen. Frank R. Lautenberg, whose death created the vacancy that led to Booker's election Oct. 16.
Booker is only the fourth black senator to be popularly elected, and the first since Obama won a seat in 2004. Others have been appointed.
Booker and his mother met with Lewis in the morning. The new senator said his eyes welled.
"It really is humbling that in the span of one generation, we as a nation have made so much progress," Booker said.
Lewis and Sen. Tim Scott (R., S.C.), the only other African American now in the Senate, attended Booker's swearing-in.
"I stand on the shoulders of giants," Booker said, referring to Lewis and other civil rights pioneers. "To have him standing there as I became one of the handful of African Americans ever to swear that oath in that chamber was something that I will never forget."
With Sen. Robert Menendez (D., N.J.) also representing New Jersey, the state is now the first to be represented by a black and a Latino senator.
Booker's mother, Carolyn, called the day "a special, special moment" and said, "I'll have my chest poked out for a long time."
"I always told my children they could be and do anything they wanted to do, that that was the beauty of America. To have dreams and be able to realize your dreams," she said. "It is just wonderful to see him realize his dreams."
She added that Booker's father, Cary, "is looking down and is equally as proud." Cary Booker died Oct. 10, six days before New Jersey's special Senate election.
Bonnie Lautenberg's front-row presence at the swearing-in - she was just seats from Booker's mother - was a surprise. Her husband had chafed at Booker's ambition, and the Lautenberg family sharply criticized Booker and endorsed a rival during the summer's Democratic primary.
Booker, though, said Lautenberg texted him shortly after the campaign.
"Gracious text messages, encouraging text messages . . . she has been nothing but supportive and encouraging and, of course, I wanted her there with my family today," Booker said.
He took over Sen. Lautenberg's old offices, where the only decorations were posters left by the former senator's staff.
Young (by Senate standards), technologically savvy, and celebrity-styled, Booker has thrived in the digital age, and he arrived in the Senate with a widespread following. He estimated that 700 friends, relatives, and supporters came to Washington for receptions and parties.
At the swearing-in, an unusually large crowd of Democrats came to shake Booker's hand, and exchange hand slaps, one-armed hugs, and occasional fist-bumps. They were so noisy that Majority Leader Harry Reid (D., Nev.) had to ask for order in the chamber.
Booker, known for his sterling biography (Stanford football, Rhodes scholar, Yale Law), famous friends (including Oprah Winfrey), and viral moments of heroism, built a national reputation as Newark's mayor, working as a relentless salesman for his long-troubled city.
But he will now have to navigate a body where young senators are expected to quietly wait their turn - though a new generation, led by Sen. Ted Cruz (R., Texas), has bucked that tradition.
Booker seemed eager to adhere, at least for a day, to Senate norms. Asked about specific issues he had discussed with Republicans, he held back, saying, "I just don't know what the mores of the Senate are yet."
He said Obama and former New Jersey Sen. Bill Bradley, a mentor of his, strongly urged him to take time to get to know his new colleagues in the clubby chamber.
Paraphrasing the president, Booker said Obama urged him to aim for singles and doubles as a newcomer, not "the grand slam."
Booker was assigned to three committees: Commerce, Science and Transportation; Environment and Public Works (both of which Lautenberg served on); and small business.
Booker, if he is reelected next year, could quickly move to other panels after 2014 races reshuffle Senate membership. He restored Democrats' majority to 55 seats, including left-leaning independents.
Booker has vowed to try to break the gridlock that has enveloped the Capitol, and cited his work with Gov. Christie.
"That reputation of working together with people is something that I hope can give me some tailwinds in working with other Republicans now," Booker said.
He quickly got a taste of Washington's gnarled politics, and the Senate's sometimes stifling pace, though.
Moments after taking his oath of office, Booker voted to advance Obama's nominee to lead the Federal Housing Finance Agency. Despite Democrats' numeric advantage, the nomination was blocked by Republicans' filibuster threat.
The blockade led to angry finger-pointing and threats of an all-out war over nominations.
Booker planned to return to New Jersey this weekend to campaign for fellow Democrats in Tuesday's election before going back to Washington to step deeper into the fray.
The Senate is expected to take up a bill on gay and lesbian rights - one of Booker's most cherished issues - next week.