The pop star took the stage at the campaign event Monday evening, where she performed a number of her anthems -- including "Dark Horse" -- for the crowd in the vital swing state.

With Election Day just hours away, Katy did take a brief pause from her lyrics to make a pro-choice declaration to the audience, shouting into the mic ... "It's my body and my choice."

She then proceeded into her next song, "Part of Me" ... hyping up the crowd, encouraging them that they're "almost" to the finish line.

Katy's appearance at the Harris rally confirmed her prior endorsement of the VP ... which she first expressed back in July after KH was tapped as President Joe Biden's replacement in the race.

At the time, Katy shared her support by resharing an edit of Harris' most viral moments set to her new anthem, "Woman's World."

However, on Monday night, Katy did a whole lot more than post on social media, showing up in person for the Democratic nominee.

The rally, which took place at Carrie Blast Furnaces in the Steel City, also featured appearances from Andra Day, D-Nice and DJ Arie Cole.

Katy wasn't the only pop star to show up for Harris in Pennsylvania Monday night, however ... Lady Gaga also campaigned on behalf of the Veep, but she hit the rally on the "Rocky" steps in Philadelphia.

As part of Harris' final campaign push, Gaga was selected to headline that event, alongside Ricky Martin, The Roots, Jazmine Sullivan, DJ Cassidy and Adam Blackstone. Oprah Winfrey, as well as DJ Jazzy Jeff and Fat Joe, were named as speakers heading into the Election Eve bash.

It's quite the deadlocked race between Harris and Donald Trump ... who has received a number of celebrity endorsements of his own.

We'll have to wait until the polls close and all the mail-in ballots are counted before a victor is named.