The 21-year-old's signing Thursday is pending United States Soccer Federation approval. Orlando City competes in the American Division of the USL Pro Division, the third tier of the American soccer system.
A Liverpool native, the midfielder most recently played with Major League Soccer's New York Red Bulls, who drafted him the second round of the 2011 draft.
Rooney appeared in five regular season games for the Bulls and made two US Open Cup appearances with them, where he scored his lone goal of 2011 against FC New York.
Orlando City was 15-3-6 in 2011, and won the US Pro Championship.