Soto walked and singled before being lifted for a pinch hitter in the third inning, elevating his average to .351 and sealing the NL lead in the category during this pandemic-shortened 60-game season.
The 21-year-old Soto surpassed Brooklyn's Pete Reiser as the youngest ever to take a batting crown. Reiser was 22 when he ended the 1941 season hitting a league-leading .343.
"For me, it doesn't matter the age," Soto said with a smile when informed of the feat's historical significance. "If you deserve it, you deserve it."
Soto was also named Washington's player of the year in voting by local media.
The Nationals finished 26-34 a year after winning their first World Series.
The Associated Press contributed to this report.