Williams debuted with the Cubs late in the 1959 season and played in a total of 30 games in both the 1959 and 1960 seasons. In 1961, he played in 146 games and was selected as the NL Rookie of the Year. That year, he hit 25 home runs and drove in 86 runs. In 1962, 1964, and 1965, he was named an NL All-Star. He won the NL Player of the Month Award in May 1964 with a .455 average, 8 HR, and 22 RBI. Williams struggled defensively in the first few years of his career, leading NL outfielders in errors as a rookie. By the mid-1960s, his defense was no longer seen as a serious weakness. He would return to the All-Star Game in 1968, 1972, and 1973.