The 34-year-old singer shared photos of herself with the 68-year-old Democratic presidential hopeful on social media after a sit-down with Clinton and her husband, former president Bill Clinton.
"Being in Vegas for #PieceOfMe is amazing for so many reasons... Especially today... because I had the incredible opportunity to meet Hillary Clinton!" Spears gushed.
"Such an inspiration and beautful voice for women around the world!!! This woman had an intense presence and I felt very honored to meet her!!!" the star added.
Despite Spears' praise, the singer reportedly deleted her endorsement for Clinton from her caption. News outlets said Spears initially included the hashtag "#ImWithHer," which is used by Clinton supporters on social media.
Clinton and rival candidate Bernie Sanders attended an MSNBC town hall meeting that evening, where both hopefuls said they'll go further than president Barack Obama on immigration. The first-ever Nevada Democratic caucus will take place Saturday.
Model Kendall Jenner and singers Demi Lovato and John Legend are among the other celebrities who have showed their support for Clinton. Spears is in residence at The Axis at Planet Hollywood Resort & Casino through 2017.