Born in Memphis, McMillon has two younger siblings. He spent his childhood in Jonesboro, Arkansas, but the family moved to Bentonville — the beating heart of Walmart's operations — when he was 16.
Growing up, McMillon attended church and played varsity basketball. McMillon told Fortune that his parents were supportive and encouraged him to develop a competitive streak.
McMillon took on his first gig at Walmart in 1984, in order to earn money for college. The high school student was responsible for unloading trucks at one of Walmart's distribution centers.
Fortune reported that the job paid $6.50 an hour. McMillon said he considered working for McDonald's, but the pay was better at Walmart.
After high school, McMillon attended the University of Arkansas, a school that boasts a particularly strong connection with Walmart.
They've even got a Sam M. Walton College of Business. But the school's name was changed to that years after McMillon graduated in 1989.
McMillon's thoughts returned to his old employer as he worked to earn his MBA from the University of Tulsa. He told Fortune that he called up a Walmart executive during his second year.
That executive was Bill Fields, a high-ranking company leader who had once served as Sam Walton's assistant. Fields told McMillon to take on a role at a Tulsa Walmart.
Fortune reported that when the business student hesitated, Fields challenged him to handle the 52-hour work week.
McMillon took Fields up on the challenge and made it work.
McMillon quickly began to rise within the retailer's ranks. As a buyer, he moved between categories like fishing gear, womenswear, diapers, crafts, and fabrics.
He even got to interact with Walton early on, when he gave a presentation on fishing gear at his first Saturday morning meeting in January 1991.
"Sam was running the meeting," he told the Associated Press. "So I got to stand next to him and show an item from our fishing department and talk about it."
The company founder and the future CEO overlapped at the company's Bentonville headquarters for about a year, according to the Associated Press. Walton died on April 5, 1992.
McMillon didn't stop at the executive level. In 2005, after working as chief merchandiser for Sam's Club, he became CEO of the members-only warehouse club.
Five years later, McMillon got another opportunity to climb within the company. He took over Mike Duke's role running Walmart International after Duke became CEO of Walmart Inc.
That move signaled that McMillon was a likely heir apparent. So, when 2013 rolled around and it was announced that McMillon would be replacing Duke on February 1, 2014, it didn't come as much of a surprise to observers.
As CEO of Walmart Inc., McMillon has focused on boosting the retailer's digital capabilities and omnichannel approach. Under McMillon, Walmart associates also saw the company's minimum wage rise to $11 an hour in January 2018.
He's also become more of a figure in the political arena, as of late.
McMillon donated $6,350 to Republican and conservative causes and figures between 1990 and 2016.
He served on US President Donald Trump's now-defunct strategic and policy forum, but has criticized the president on the issue of tariffs and his reaction to the Unite the Right rally in Charlottesville.
McMillon and his wife, Shelley, have two sons. He earned over $22 million in 2018, according to Bloomberg.
"Having been here a long time, I think I had the feeling that I knew what responsibility felt like," McMillon told Fortune on his first day as CEO in 2015. "And then you move into the role and you find out there's a whole 'nother level of it."