The Associated Press obtained a copy of remarks that Kaine plans to deliver Saturday at a breakfast of Democratic activists in Columbia, South Carolina.
In the remarks, Kaine says the former first lady and U.S. senator from New York is a "classic American optimist" who can lead the U.S. "in a very complicated world."
"She understands the challenges facing Americans from all walks of life and has the compassion and skill necessary to help improve our everyday lives," Kaine says.
Kaine's endorsement is the latest show of support for Clinton, who has led by wide margins in early presidential polls of Democrats and could limit the field if she decides to attempt to become the first female president.
As she considers whether to run, Clinton's popularity among Democrats has essentially frozen the field of potential challengers, which could include Vice President Joe Biden, Maryland Gov. Martin O'Malley and former Montana Gov. Brian Schweitzer.
Clinton has said she will decide whether to seek the White House again later this year and plans to embark on a national tour in June to promote a memoir about her State Department years. She is expected to campaign for Democrats before the fall midterm elections.
Kaine, a former Virginia governor, was scheduled to speak at the South Carolina Women's Democratic Council breakfast and headline the state party's annual Jefferson Jackson dinner later Saturday. South Carolina traditionally holds the first presidential primary in South, following contests in Iowa and New Hampshire, and hardcore Democrats were pivotal in helping Obama trounce Clinton in the state's 2008 primary.
In his remarks for the breakfast, Kaine pointed to Clinton's work on domestic and foreign policy and said he was supporting Clinton because she was "the right person for the job." But he said early involvement was necessary because helping her get to the White House "will still be hard."
"If it were easy for women to achieve top leadership spots in this country, Congress would have more than 18 percent women serving. More than 5 percent of Fortune 500 companies would have a women CEO. And women would be seated on more than a quarter of the federal benches across the country," Kaine said.
He is the latest prominent Democrat to encourage Clinton to run for president. Other Clinton backers include Sen. Chuck Schumer of New York, former Michigan Gov. Jennifer Granholm and Sen. Claire McCaskill of Missouri.