Per Howard Fendrich of the Associated Press, Soto will play left field and is hitting fourth in the lineup.
"He said he's ready," Nationals manager Dave Martinez said, according to Fendrich.
Hours before the Nationals' season opener against the New York Yankees on July 23, the team announced Soto had been placed on MLB's COVID-19 injured list after his test came back positive.
General manager Mike Rizzo told reporters at the time that Soto was asymptomatic.
ESPN's Jeff Passan reported on July 29 that Soto had received clearance from MLB to play after returning two negative tests, but the outfielder had to get approval from Washington, D.C., health officials to get back on the field.
Soto told reporters last week he believes the initial positive test was a false positive: "I've been working on it. I've been tested a bunch of times negative. I've been following the rules, being in the right spot. And I think that's why I think it was fake positive. I've been following the rules, I've been really serious with this because it is out there."
The Nationals defeated the Mets 5-3 in Tuesday's series opener. The reigning World Series champions are off to a 4-4 start, but the offense without Soto is tied for 24th in runs scored (29).
Soto should provide a significant boost in the middle of the lineup. The 21-year-old hit .282/.401/.548 with 34 home runs, 110 RBI and 12 stolen bases in 150 games in 2019.