Reese Witherspoon reacted to Joe Biden's naming of Kamala Harris as his running mate in the 2020 presidential election with a story about her childhood political aspirations.

Long before Witherspoon, 44, became a big name in Hollywood, the "Little Fires Everywhere" actress had big dreams of assuming the Oval Office, she shared in a new Instagram post.

"I woke up this morning thinking about a moment from my childhood. In the 3rd grade our teacher asked us what we wanted to be when we grew up, I raised my hand and said, 'I want to be the first female President of the United States of America," she captioned an adorable throwback pic on Instagram.

JESSICA CHASTAIN REVEALS KAMALA HARRIS DOLL HER DAUGHTER, 2, PLAYS WITH: 'HELLO, MADAM VICE PRESIDENT'

While some of her classmates "laughed" in response, she noted, Witherspoon said her teacher voiced support.

Witherspoon went on to discuss the current political climate and championed Harris, 55, for being named by Biden as his vice presidential nominee.

"My thoughts today are with woman (sic) in our country, especially the young Black and Brown girls of our nation. Who have watched their mothers hold up their families, their communities, their cities, their states. Now you know that YOU too can work hard, dedicate your life to service and show up every day to help others, and YOU can RISE to become a Vice Presidential nominee in the United States of America. Today is truly a historic day!" she added.

Witherspoon also shared her support for Harris by using the hashtags #KamalaHarris and #WeHaveHerBack in the post.

CELEBRITIES REACT TO KAMALA HARRIS BEING ANNOUNCED AS JOE BIDEN'S RUNNING MATE: 'EXCITED TO VOTE'

Biden first tapped Harris as his running mate in an email to supporters on Tuesday.

Presumptive Democratic presidential nominee Joe Biden and Sen. Kamala Harris, D-Calif., speak a campaign event at Alexis Dupont High School in Wilmington, Del., Wednesday, Aug. 12.

Presumptive Democratic presidential nominee Joe Biden and Sen. Kamala Harris, D-Calif., speak a campaign event at Alexis Dupont High School in Wilmington, Del., Wednesday, Aug. 12. (AP/Carolyn Kaster)

"I’ve decided that Kamala Harris is the best person to help me take this fight to Donald Trump and Mike Pence and then to lead this nation starting in January 2021," the Democratic presidential candidate wrote.

"I need someone who understands the pain that so many people in our nation are suffering. Whether they’ve lost their job, their business, a loved one to this virus. This president says he “doesn’t want to be distracted by it”. He doesn’t understand that taking care of the people of this nation -- all the people -- isn’t a distraction -- it’s the job. Kamala understands that," Biden, 77, continued.

Biden's selection marks just the third time in history a woman has been chosen as a running mate on a major party presidential ticket and the first time a Black and South Asian woman is elevated to the role.

Celebrities flocked to social media to congratulate Harris and show their support for the 2020 ticket. Among them were Hollywood couple John Legend and Chrissy Teigen, Patton Oswalt, Mindy Kaling and Rob Reiner.

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Rosie O'Donnell, known for her public criticism of Trump, wrote, "AMEN!!" on Twitter.

Meanwhile, Maya Rudolph, who has done impressions of Harris on "Saturday Night Live," told Entertainment Weekly on Tuesday: "Oh s--t, ruh-roh," shortly after Biden's announcement.

Fox News' Jessica Napoli contributed to this report.