During the toughest moments of the Democratic presidential race last winter, when neither polls nor primaries were going his way, Joe Biden always had at least one thing to look forward to.

Nearly every day, his traveling chief of staff, West Roxbury native Annie Tomasini, would bring in a close friend or family member to surprise him on the campaign bus or plane. Whether it was his sister, Valerie Biden Owens, one day, a grandchild or two the next, or his former personal aide Fran Person, someone would be there to boost his spirits during the difficult stretch of setbacks before his first victory in South Carolina.

“She always had a plan to make the campaign trail go better,’’ said Bruce Reed, the president-elect’s former chief of staff. “In part that was to make the long, hard grind more fun for him, but it was also because [Biden] really wanted to share the experience with them.’’

Now, Tomasini, a 41-year-old former Boston Latin and Boston University basketball star, is taking her Biden-whispering skills to the White House — skills that were further tested when she became one of just a handful of aides to see Biden in person in the early days of the pandemic. She will be director of Oval Office operations in the Biden White House — a crucial behind-the-scenes job that traditionally involves ferociously guarding the president’s time while simultaneously trying to keep the leader of the free world roughly on schedule each day.

In some ways, it’s tough to imagine a harder job than being a gatekeeper for Biden. He lives for the boundary-less ropeline after events: grinning for every imaginable selfie, asking for phone numbers, and urging voters to call a loved one who couldn’t be there so he can say “hi’’ to them on FaceTime. (This is all pre-COVID, of course.) Senator Lindsey Graham once joked to Politico that Biden’s former personal assistant’s greatest skill was in “gently persuading the vice president it was time to end the meeting.’’

But Tomasini, who first began working for Biden when he launched his second presidential bid almost 15 years ago, leans into his gregariousness, and sees her job more as connecting him with the right people instead of keeping people away, according to those who’ve worked with her.

“She’s a big believer in letting Biden be Biden,’’ said Reed. “Annie helped make sure that those people not only had a few minutes with him but stayed part of his life.’’

Those interactions may have contributed to Biden’s chronic lateness on the trail, but they also boosted the candidate’s mood — and have their political advantages. For example, a spontaneous stemwinder of a conversation with a young fan named Brayden Harrington who saw Biden speak in New Hampshire in February led to a bond between the two over Harrington’s stutter — an impediment Biden also struggled with as a boy. The 13-year-old eventually delivered a speech at the Democratic National Convention in August about overcoming his stutter that became a highlight of the event.

“We find a way to balance these things but we also find a way to prioritize these things,’’ Tomasini said in an interview with The Boston Globe, referencing Biden’s many spontaneous connections with people. “They’re amazing to see, they really are.’’

Being the traveling chief of staff to a presidential candidate by definition involves a breakneck pace, an endless string of events, meetings, and decisions, with anonymous hotel rooms and suspect road food thrown in for good measure.

But in the unusual and at-times soul-crushing year of 2020, Tomasini spent many weeks not aboard a campaign jet, but in Wilmington, Del., where the pandemic had grounded Biden in early spring.

She became one of just a handful of aides allowed in his home, and circumstances forced her to take on the jobs of others in the army of staffers who would normally assist a presidential candidate. Every Zoom appearance, TV interview, or important phone call required Tomasini, with the help of Biden’s personal aide Stephen Goepfert, to do the prep work that would normally be handled by a larger staff.

“Get your visual of the most important person in the world and get a picture of their office and think about how many people are outside his or her office,’’ said former senator Ted Kaufman, a longtime Biden friend and adviser. “In this visual, it’s Annie.’’

The pressure is still on Tomasini to perform multiple roles even during the transition, which Biden has spent in Wilmington with the pandemic still raging. Wielding a phone and an iPad, she is responsible for running traffic control on the many important people attempting to reach Biden all day, and has to make countless snap decisions on who should get through and who can wait. (The only clear rule? Family always gets through first.) If Biden needs to reach a world leader or a governor, that often falls to Tomasini.

“She’s like his interface with his world every day all day,’’ said Kaufman. With Biden’s chief of staff, Ron Klain, and others working remotely, “you can make the argument that she’s basically the chief of staff,’’ he added.

Tomasini is eerily calm amid chaos, friends and co-workers say, but also brings a lighthearted approach to her hectic job — and seems never to run out of energy or burn out. She runs marathons in her “spare’’ time, cracks jokes, and doesn’t appear to ever take a day off.

The job requires total dedication, with Tomasini often unable to see her family and friends so as not to risk bringing the virus into the 78-year-old Biden’s bubble. Friends sometimes asked for “proof of life’’ texts when they checked in on her.

“I would get these texts randomly at different times and they were just a couple of words,’’ said Katie Lapp, a friend and executive at Harvard who worked with Tomasini before she joined Biden’s campaign. “ ‘Hanging in there.’ ‘I’m still here.’ ’’

That’s why Tomasini’s new White House job, though a big one, may be relatively relaxing compared to the work she did in Biden’s basement in Wilmington. She’ll have an in-person staff assisting her, for one thing. But it’s still a delicate role that can greatly affect the environment of a White House.

It likely will be very different from the atmosphere now. Donald Trump’s Oval Office is known for loose protocols, with all sorts of people obtaining access to the president. Trump’s former director of Oval Office operations, Madeleine Westerhout, was promoted from her job as his personal secretary but then was fired after only a few months after Trump learned she shared personal information about him to reporters off the record, including, reportedly, that he called one of his children fat. His former body man Nick Luna, who contracted COVID-19 during the White House outbreak in October, now holds the role.

In a sense, Tomasini has trained her whole life for the job.

She has deep political roots in Boston. Her grandmother, Rita Walsh-Tomasini, was elected president of the Boston School Committee when Tomasini was a child, and her great uncle was a state senator from Dorchester. “I was at campaign events early days and would campaign with my nan,’’ Tomasini recalled. That exposure piqued her interest in politics, which she studied at BU — where she attended on a scholarship — in between her packed schedule as co-captain of the women’s basketball team.

Her former teammate Marisa Mosley, who now coaches the BU women’s team, remembers Tomasini as “nurturing’’ but tough, a player who could both attack the rim or sink three-pointers. Tomasini once broke her nose during practice, but kept playing with a wraparound plastic mask for weeks. Mosley sees a similar grit in her former teammate now.

“I swear I brag about her all the time because I know the sacrifices she had to make to get where she’s at,’’ Mosley said. “As a woman, you’ve got your family sacrifice, your friend sacrifice because the job begs of you to be present all the time. You don’t get to turn it off — you don’t get weekends. It’s not a 9 to 5. I was always proud and also in awe of that kind of dedication.’’

After graduating college in 2002, Tomasini became executive assistant to Larry Rasky, a longtime Biden confidant and Boston public relations executive. He worked on Biden’s 1988 and 2008 presidential runs and later launched a super PAC to support his 2020 bid.

The job could be hectic and grueling, as she had to coordinate the chaotic schedules of three partners of the firm — Rasky, Joe Baerlein, and Ann Carter — all with big personalities. “There were other admins who would . . . come into my office crying,’’ said Carter. “Annie was unflappable.’’

It was there that Rasky’s constant stories about Biden piqued Tomasini’s interest.

“He talked about Joe Biden all the time, all the time,’’ Tomasini said. “[Biden] was sort of the third senator from Massachusetts in the offices.’’

Tomasini got her chance to meet Biden when Rasky’s firm hosted an event for him during the 2004 Democratic National Convention in Boston. Her job was checking names at the door.

“I was completely nervous,’’ she said. “Larry overstated what I had done to help put the event together. [Biden] said, ‘Well you need to come work with me in Washington.’ ’’

In the gray-haired world of Biden’s inner circle, Tomasini counts as a relatively “new’’ — and young — entrant. It was Rasky vouching for her that got her in the door.

“I think the reason that Annie got started with us was primarily because Larry said this is really a keeper,’’ Kaufman said.

Tomasini jumped aboard Biden’s 2008 presidential campaign as national deputy press secretary after working her way up to managing the Washington office of Rasky’s firm. In Iowa, she was part of a small team that spent hours in the car driving with Biden to nearly all of Iowa’s 99 counties.

After Biden was elected vice president, she followed him to the White House as a deputy press secretary in his office. But a few years later, she decided to head back to Boston to take a job at Harvard managing community and government relations, primarily for the university’s Allston development project.

“I said, ‘Annie, why’d you jump off the bus?’ ’’ recalled Baerlein, her former boss. “She said, ‘It’s hard to keep up with Joe Biden.’ ’’

In Boston, she was surrounded by her family and friends, which made leaving to join Biden again when he decided to run in 2019 a tough decision.

But Drew Faust, the president of Harvard when Tomasini worked there, wasn’t surprised when Tomasini left because she knew how important the former vice president was to her. “She took the harder path,’’ Faust said.

That path has led her to a top job in the White House, but it also came with its share of tragedy, too. Her former mentor Rasky died of COVID-19 last spring at the age of 69.

“When he won the election, I called Carolyn, his wife, literally after I called my parents because I know how much this would have meant to Larry,’’ said Tomasini. “He loved Joe Biden so much. He is still celebrating the victory wherever he is.’’

Liz Goodwin can be reached at elizabeth.goodwin@globe.com. Follow her on Twitter @lizcgoodwin.