As Williams was a pitcher in high school, he made eight starts in his first professional season with the Gulf Coast League Braves, compiling a 1–0 record and 3.10 earned run average.

He debuted with the Atlanta Braves that September, and batted .368 in ten games split pretty evenly between first and third base.

On May 23, Williams entered a 4–0 loss to the New York Mets at Shea Stadium as a pinch hitter in the eighth inning, and remained in the game at catcher.

George Foster led off the Reds' half of the second inning with a single, then proceeded to take full advantage of Williams' inexperience at his new position.

On September 10, Williams became the only Braves player besides Hank Aaron to hit a home run into the upper deck at Fulton County Stadium.

However, he also had 28 home runs and 87 RBIs, drawing the attention of the Baltimore Orioles who acquired him along with Taylor Duncan from the Braves for Davey Johnson, Pat Dobson, Johnny Oates and Roric Harrison on the last day of the Winter Meetings on December 1, 1972.

[11] Many Oriole players, most notably ace pitcher Jim Palmer, were critical of this trade, but because they had finished 9th in runs scored in 1972 (behind every team except lowly Texas, Milwaukee, California, and Cleveland), it made sense to send an aging replaceable second-baseman (Bobby Grich moving in for Dave Johnson), a back-end-of-rotation starter (Pat Dobson), and 2 throw-ins to insure a prime bat at a position in which their division rivals were killing them (Freehan, Munson, Fisk).

Williams batted .237 with 22 home runs (almost double that of the next Oriole, with 12) and a team-leading 83 RBIs his first season in the American League.

Williams reached the post season for the only times in his career with the Orioles in 1973 and 1974, losing to the Oakland Athletics in the American League Championship Series both years.