Lasher debuted in the major leagues with the Twins at age 21 in 1963. Over six major league seasons, Lasher appeared in 151 games (all but one as a relief pitcher) and had a record of 11–13 with a 3.88 earned run average. In 1968, Lasher appeared in 34 games for the American League pennant winning Detroit Tigers, finishing with a 5–1 record and a 3.33 earned run average.
He also pitched 2 scoreless innings in the 1968 World Series to help the Tigers beat the St. Louis Cardinals. In 1970, Lasher pitched in a career-high 55 games for the Tigers and Indians. His major league career ended in 1971, when he appeared in 2 games for the Angels and gave up 4 earned runs in 1⅓ innings for a 27.00 earned run average.