Mackenzie “Mackie” McDonald began playing tennis at age three with his dad and attended Piedmont High School in California, the same high school as former World No. 4 Brad Gilbert. McDonald played college tennis at UCLA (2014-16), winning 2016 NCAA singles and doubles titles before turning pro and finished 2016 college season as No. 1 singles and doubles player in nation.
McDonald broke into Top 50 in February 2022 and achieved career-high No. 48 in August 2022 after undergoing right hamstring surgery in 2019 and falling out of Top 250 in 2020. Mackie was voted ATP Comeback Player of the Year by his fellow players in 2021.