Williams will serve as the Rangers' opening pitcher ahead of Kumar Rocker during Friday's game against the Rays.
Williams inked a major-league deal with Texas on Tuesday after he was cut by the Nationals last weekend. The right-hander worked in bulk relief with Washington and threw a season-high 63 pitches on two occasions across eight total appearances. Rocker has worked behind an opener twice this season, allowing just two runs on eight hits and three walks with 16 strikeouts across 12.2 innings.