Jones has spent the last 11 seasons as the Orioles' primary center fielder since being traded from the Seattle Mariners in 2008.
The 33-year-old is hitting .281/.310/.430 with 12 home runs in 108 games this season.
Jones was the subject of trade rumors ahead of the July 31 non-waiver deadline. Unlike many of his former teammates, including All-Stars Manny Machado and Jonathan Schoop, Jones remained in Baltimore with the team entering a rebuild.
Shortly before the positional change was officially announced by the team, the four-time Gold Glove winner tweeted his support of the move.
Mullins, the Orioles' No. 9 prospect, will hit ninth and play center field Friday against the visiting Boston Red Sox.
Between 108 games at Double-A and Triple-A this season, Mullins is slashing .288/.346/.465 with 11 homers and 21 stolen bases.
The 23-year-old was greeted by Jones with a hug when he entered the Orioles' clubhouse Friday, according to Jon Meoli of the Baltimore Sun.
"Coming from a guy with 10 years under his belt, being a huge veteran, a huge team leader for all these years, being in direct contact with him for a huge moment in both of our careers, it's been amazing. ... He's been very supportive with me playing center field," Mullins said. "We've had a lot of contact about it, with him just kind of guiding me through that process."
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