A right-hander, he batted left-handed and was listed as 6 feet 1 inch (1.85 m) tall and 202 pounds (92 kg).

In 1963, Ackley won 18 games and lost only five for the Indianapolis Indians of the Triple-A International League and was named Pitcher of the Year; his team went on to win the Governors' Cup playoff title.

In the closing weeks of that season, at age 26 and in his ninth year in pro ball, he made his Major League debut with two starting pitcher assignments, with a no-decision on September 21 against the Detroit Tigers, followed by his first and only MLB victory six days later, a seven-inning, 7–1 triumph against the Washington Senators.

He was purchased by the St. Louis Cardinals on November 24, 1964, but did not make it back to the major leagues.

In his five big-league games, Ackley posted a 1–0 career won–lost record and a 4.19 earned run average, permitting 17 hits and 11 bases on balls, with 17 strikeouts, in 191⁄3 innings pitched.