Fiorina is likely to be the only prominent woman to seek the party's nomination, with Carson the only likely African- American.
Both Fiorina and Carson have the potential to help the Republican win over a more diverse group of supporters in 2016.
Both candidates begin the race as underdogs in a campaign expected to feature several seasoned politicians, among them former Florida Gov. Jeb Bush, Wisconsin Gov. Scott Walker, along with Florida Sen. Marco Rubio and Texas Sen. Ted Cruz.
The Republican field is already more diverse than it was four years ago. Fiorina and Carson will compete against Republican counterparts Rubio and Cruz, each vying to become the first Hispanic president. And most of the candidates are in their 40s and 50s.
Still, the Republican National Committee has acknowledged a pressing need to broaden the party's appeal beyond its traditional base of older, white men. President Barack Obama won re-election in 2012 with the strong support of women and ethnic minorities, who are becoming a larger portion of the American electorate.
She also directly criticized Democrat Hillary Rodham Clinton, the front-runner for her party's nomination.
"I have a lot of admiration for Hillary Clinton, but she clearly is not trustworthy," Fiorina said, after confirming her plans to seek the presidency.
