Clinton made her announcement on Friday, just days before the Democratic National Convention
Credit: Melina Mara/The Washington Post via Getty Images

He’s with her.

Hillary Clinton announced on Friday that Virginia Senator Tim Kaine will be her running mate as she attempts to clinch the White House in November.

“I’m thrilled to announce my running mate, Tim Kaine. Tim is a lifelong fighter for progressive causes and one of the most qualified vice presidential candidates in our nation’s history,” Clinton captioned a photo of the two fist-bumping at one of her rallies. “But his credentials alone aren’t why I asked him to run alongside me. Tim’s a man of relentless optimism who believes no problem is unsolvable if you’re willing to put in the work.”

She continued: “That commitment to delivering results has stayed with him throughout his decades-long career as a public servant. I could give you a laundry list of things he accomplished as mayor of Richmond, governor of Virginia, and in the United States Senate. But here’s what’s important: Tim has never taken a job for the glory or the title.”

Clinton’s vetting process began over a year ago when she had a list of more than two dozen potential VP picks, but she and Kaine only recently got to know each other better. He was among the handful of VP finalists Clinton met with recently, a Clinton campaign official tells PEOPLE. While some of those private meetings leaked, Kaine’s managed to slip under the radar.

Although many were under the impression that Clinton was leaning towards Senator Elizabeth Warren as a running mate, PEOPLE has learned that Clinton had multiple follow up meetings with Kaine – including one where his wife joined the Clintons and their daughter Chelsea and her husband for dinner – and enjoyed his humble persona at her recent campaign appearance in Virginia, which she alluded to in her Instagram announcement.

“He’s the same person whether the cameras are on or off, motivated by the belief that you can make a difference in people’s lives through public service,” she added. “I didn t make this decision lightly. I’ve had the privilege of seeing two presidents and two vice presidents up close, and I wanted to pick someone who will be able to give me their best advice, look me in the eye, and tell me they disagree with me when they do.”

The campaign source said that what Clinton prioritized in picking Kaine was his readiness to do the job and the fact that the pair got along well both personally and professionally.

Clinton asked Kaine to join her ticket – and he accepted – in a phone call Friday evening.