The Team Fortress 2 squad contains characters, upgrades and abilities from the Valve shooter, and can be used in any version of Hero Academy once unlocked.
Purchasing the PC port also unlocks cosmetic items in Team Fortress 2.
In a statement praising Valve's vision, Robot Entertainment's Patrick Hudson said: "Working with Valve on this major franchise and bringing their popular characters into our world is groundbreaking in the world of gaming.
"It marks the first time we've seen a major crossover of characters from the PC to mobile devices and from the first-person shooter genre to turned-based strategy."
Hero Academy is a turn-based strategy game in which players attempt to destroy their opponent's crystals.