The Pirates promoted Johnson from High-A Greensboro to Double-A Altoona on Sunday, Andrew Destin of the Pittsburgh Post-Gazette reports.
The 20-year-old will move up to Altoona after slashing .236/.369/.382 with 13 home runs and 20 stolen bases across 489 plate appearances with Greensboro. Johnson has split time between second base and shortstop this season, but the keystone will likely be his long-term home once he reaches the big leagues.