The 6-foot-4 right-hander, originally picked in the fourth round of the 2010 Draft by the Nationals, will be rejoining Washington after being acquired from Oakland on Wednesday in a three-team deal. Another right-hander, Class A Advanced Stockton's Blake Treinen, and a player to be named, were included with Cole.
The A's received slugger Michael Morse in exchange for the trio and then turned him over to Seattle for catcher John Jaso.
Cole, who turned 21 earlier this month, spent last season in the A's system after the Nationals included him in the deal that brought Gio Gonzalez to Washington. He was Oakland's fourth-ranked prospect.
The Florida native began the season in the California League, where he scuffled to an 0-7 record and a 7.82 ERA in eight starts.
He steadied things upon a demotion to Class A Burlington, however, turning in a 2.07 ERA over 95 2/3 innings to finish out the season. He struck out 102 while walking just 19. In 133 2/3 total frames, he registered a 3.70 ERA with 133 strikeouts and 29 walks.
Treinen, a seventh-rounder in 2011 out of South Dakota State University, spent the entire year in Stockton, going 7-7 with a 4.37 ERA, striking out 92 and walking 23, in 103 innings.