He played in Major League Baseball (MLB) for the St. Louis Cardinals, Chicago Cubs, and Montreal Expos.

A native of Ilion, New York, Day played Major League Baseball for all or parts of six seasons (1969–74), with the bulk of that time spent with the Montreal Expos.

He made the Cubs' opening day 1970 roster, but was soon traded again, in May, to Montreal for veteran catcher Jack Hiatt.

But the following season, after the Expos acquired veteran center fielder Willie Davis in an offseason blockbuster trade with the Los Angeles Dodgers, Day lost his semi-regular job.

Day retired from coaching on September 13, 2021, age 74, after a winning game with the Evansville Otters against the Lake Erie Crushers with a final score of 3–1.