Brat, an economics professor at Randolph-Macon College in Virginia, beat 14-year incumbent Cantor with 55.6 percent to 44.5 percent of the vote.
Palin called the victory "encouraging" and an indicator of how things will play out in the midterm elections.
"Congratulations to Dave Brat in Virginia on such an encouraging victory tonight! You shocked the political world and reminded D.C. that power lies with We the People and not any conventional party establishment," Palin wrote on Facebook early Wednesday morning.
"Dave Brat was massively outspent (more than 10 to one) and laughed off by most, but he won the trust of voters the old fashioned way -- one by one. Tonight's victory showed the power of the local grassroots -- the ones with boots on the ground who put up the campaign signs and go door to door to provide needed support for great candidates," she added.
"Grassroots commonsense conservatives can use this momentum to push good candidates like Chris McDaniel, T.W. Shannon, and Rob Maness to victory for America," Palin wrote. "These candidates are also being massively outspent by establishment candidates and they need our help and energy."