White House spokeswoman Kayleigh McEnany tweeted on Thursday that Cain "embodied the American Dream and represented the very best of the American spirit".
"We will never forget his legacy of grace, patriotism, and faith," McEnany added.
In a separate tweet, Vice-President Mike Pence called Cain "an indispensable voice for the Conservative movement" who will be "deeply missed".
Cain, who had hoped to become the first Black politician to win the GOP nomination, was initially considered a long-shot candidate.
His bid was propelled forward in September 2011 when he won a straw poll vote in Florida, instantly becoming an alternative candidate for Republican voters concerned that former Massachusetts Governor Mitt Romney was not conservative enough.
But Cain struggled to respond to accusations that he had sexually harassed several women and — in a video that went viral on the internet — rambled uncomfortably when asked whether he supported or opposed President Barack Obama's policies in Libya.
There were also gaffes on abortion and torture that led Cain's critics to question whether he was ready for the White House.
Just as Cain started surging in the polls, Politico reported that the National Restaurant Association paid settlements to two former employees who claimed Cain sexually harassed them while he was CEO and president of the lobbying group from 1996 to 1999.
Another woman, Sharon Bialek, said that Cain, an acquaintance, groped her in a car in July 1997 after they'd had dinner in Washington. Bialek, who was then unemployed, said she had contacted Cain seeking job advice.
Cain said he could not remember Bialek and denied sexually harassing anyone, but polls conducted in the weeks afterward showed his popularity slipping considerably.
Cain honed his speaking skills in the corporate world, then hosted a radio talk show in Atlanta that introduced his political views and up-by-the-bootstraps life story to many tea party supporters and other conservatives.
- Associated Press
