Holton's contract was selected by the Diamondbacks on Thursday.
Holton began the year at Triple-A Reno and posted a 6.75 ERA and 2.13 WHIP in eight innings over five relief appearances. He'll be available to make his major-league debut out of the bullpen after J.B. Wendelken (undisclosed) was placed on the injured list and Tyler Gilbert was optioned to Reno. However, it seems unlikely that Holton will pitch in high-leverage situations.