Darwin signed with the Angels as a pitcher in 1962. That year with San Jose (California League) he struck out 202 and walked 149 in 153 innings. His control problems and disabling injuries contributed to his gradual switch to the outfield starting in 1966.
The Twins made Darwin their regular centerfielder in 1972, and although he showed good power over the next three seasons (22, 18, and 25 HR), he led the AL in strikeouts each year (145, 137, 127) and had fewer fielding chances than any other centerfielder. In 1974 he tied for fourth in HR and was fifth in RBI (94). Traded to Milwaukee in 1975 while hitting .219, he was never again a regular, and he finished his career with more strikeouts than hits.