The Nationals selected Harris' contract Thursday.
The 29-year-old right-hander will be part of the Nationals' Opening Day bullpen after he impressed in spring training, where he allowed just one earned run on three hits and two walks while striking out seven over 10 innings in Grapefruit League play. Harris will likely begin his first stint in the big leagues as a low-leverage arm but could quickly work his way up the pecking order in Washington.