"Onward Together" will support civic activism and foster political resistance, its website said. Clinton's presidential election loss to Trump forced her to re-evaluate her role in a changing political environment.
The statement on the "Onward Together" website launched on Monday said the organization "will advance progressive values and work to build a brighter future for generations to come."
"There's no telling what we can achieve if we approach the fights ahead with the passion and determination we feel today, and bring that energy into 2017, 2018, 2020, and beyond," it added.
The statement also alluded to the protests against US President Donald Trump that have taken place since he entered office in January.
"In recent months, we've seen what's possible when people come together to resist bullying, hate, falsehoods and divisiveness, and stand up for a fairer, more inclusive America," it read.
The newly launched site reminded visitors that 66 million American voters had cast ballots for Clinton in the 2016 presidential election - some 3 million more than those cast for President Trump.
"Onward Together" marks Clinton's return to the political arena after her bruising loss to Trump in the November 2016 presidential election.
Despite receiving a greater number of popular votes, Clinton failed to win the Electoral College, the deciding factor in US presidential elections.
The loss came after a bitter campaign that had highlighted deep divisions within the Democratic Party, as many felt Clinton would not be an effective proponent of change. It also saw her campaign team battered by an email hacking suspected to have come from Russian operatives.
Clinton was also dogged by an investigation into her use of a private email server. She recently argued that she would have won the election had then FBI director James Comey not made public the agency's decision to reopen an investigation on the matter shortly before the election date.
Clinton used Twitter to announce the kickoff of "Onward Together," whose name is a variation of her campaign slogan "Stronger Together."
She also highlighted some of the activist groups that "Onward Together" would support including Color of Change, an organization aimed at achieving justice for African-Americans, Emerge America, a training program for aspiring female Democratic candidates, and Swing Left, a grassroots network to recapture the House from Republicans in the 2018 midterm elections.
In an email, Clinton said her organization would provide direct funding as well as message outreach for civic groups.
The 69-year-old politician tweeted that "Onward Together" had earned the backing of Howard Dean, a former Vermont governor who ran for presidential office in 2004 as a left-leaning Democrat.
Clinton has maintained a low profile in 2017, considering the next step to follow on from her previous positions as secretary of state (2009-2013), US senator from New York (2001-2009), and first lady (1993-2001).
Her decision to launch her own organizations means she will relinquish her leading role in the Clinton Foundation alongside her daughter Chelsea Clinton and her husband, former President Bill Clinton.
cmb/cmk (AFP, AP)