"The status quo has got to go, and in Alaska the man who understands this key to our state and country's future also has the guts, wisdom, experience and optimism to fight for what is right — and win," said Palin, the GOP’s 2008 vice presidential nominee, in a statement to Fox News on Friday.
Miller immediately began fundraising off the announcement, sending an email pitch to supporters.
Miller is running against Alaska Lt. Gov. Mead Treadwell and Alaska Department of Natural Resources Director Dan Sullivan for the Republican nomination.
Sullivan is the favorite to win on Tuesday and take on incumbent Sen. Mark Begich (D-Alaska) in the general election.
The announcement comes just one day after Miller, at a Thursday night debate, said he would back either of the two other GOP candidates if they win the nomination.
Miller, a former Senate nominee, beat Sen. Lisa Murkowski (R-Alaska) in the 2010 primary. But he lost to her in the general election when she ran as a write-in candidate. Palin had endorsed Miller in the primary that year.
A recent poll from left-leaning Public Policy Polling found that Begich leads all three potential Republican nominees for the general election, with his largest lead, 13 percentage points, being over Miller.
Among those surveyed, 59 percent had an unfavorable opinion of Miller, while 22 percent had a favorable opinion and 19 percent were unsure.
Since the 2010 midterms, Palin has supported dozens of candidates, with mixed results. In 2012, Palin she backed Sen. Ted Cruz (R-Texas), who has been one of the most outspoken critics of President Obama.
Endorsing him Friday, Palin said Miller could also "stop Barack Obama's fundamental transformation of the nation we love.”