The 26-year-old was a third-round pick in the 2007 amateur draft. He was on Cincinnati's Opening Day roster last year, then was sent to Triple-A Louisville on May 22.
Soto was called up from July 12 to July 19, made four starts and had three hits in 30 at-bats.
The Reds assigned him outright to Louisville after the season. He became a free agent and signed a minor league deal with the Reds in December.
Soto has appeared in four spring training games with the Reds, going 2-for-7.