Basallo had already been under team control for the next six years, but the new deal extends him for another two with a club option for 2034, making him an unrestricted free agent in 2035 when he'll be 30.
The deal can max out at $88.5 million, making it the largest pre-arbitration deal for a catcher in MLB history.
Basallo made his MLB debut this past weekend during the team's series against the Houston Astros.
The 21-year-old was the league's No. 1 catching prospect and No. 8 overall.
Basallo is hitting .286 since his debut, going 4-14 at the plate with five RBI. He would've had his first home run during his debut against the Astros, but was robbed of it.
The Dominican Republic native was slashing .270/.377.589 with 23 home runs and 67 in Triple-A this season. Basallo is currently the starting catcher for the Orioles after the team placed Adley Rutschman on the 10-day injured list with an oblique strain.
He has at least one RBI and/or one hit in each of the three games he has been in the starting lineup for. The only time he didn't record a hit was when he was brought in during Sunday's game for a single at bat.
Baltimore is now 4-1 since calling up Basallo and have outscored opponents 24-13.