Yesterday she made a confident, authoritative debut for Biden, immediately adding extra vigour to the team, tackling US President Donald Trump like a prosecutor before the jury.
The US-born daughter of immigrants - a Jamaican father and Indian mother - is already a historic pick as the first black and South Asian woman to be part of a major party ticket.
To really bust the glass ceiling, the Democratic candidates first have to win, and that is not a given against Republican Trump and Vice-President Mike Pence.
Biden leads in poll averages but the margins have tightened slightly since June and there are still party conventions and debates to go. The voting process is under a coronavirus cloud. Trump is also arguing against mail ballots. Polls mean nothing if people do not actually vote.
There have been two previous female vice-presidential candidates, Geraldine Ferraro in 1984 and Sarah Palin in 2008, but both were on losing tickets. The first female nominee for a major party, Hillary Clinton in 2016, also lost.
US voters have seen several female Secretaries of State, but no woman in the deputy role a heartbeat away from the presidency. Harris, at least at yesterday's rollout, looked the part.
Maybe actually seeing a woman performing that job could make it easier in the future for US voters to imagine a woman behind the Resolute desk.
With Biden, 77, possibly likely to serve only one term if he wins, Harris, 55, would be in the box seat to succeed him. The former San Francisco district attorney and California attorney-general has the qualifications and experience. Time is on her side.
Harris, like former President Barack Obama before her, is a progressive moderate rather than a more ideological figure. In the Democratic primary, she struggled to project a defined, authentic sense of who she is. In the general election it makes her a harder target for opponents to pin down, especially as she is working on a party agenda rather than her own.
And like Obama, Harris has charisma, an interesting life story with time spent overseas in her youth and is a trailblazer. The historic nature of her selection could draw in at least some of the younger voters who preferred other primary candidates and are more motivated to vote against Trump than for Biden.
After a drawn-out selection process, Biden appears to have made a solid choice who will also deliver excitement and promise. He's put down a big deposit on his vow to build an Administration that looks like diverse America.
With the selection of Harris the party lines are starkly drawn between two different visions of the country.
