Singer made his major league debut with the Los Angeles Dodgers on September 24, 1964, allowing one run in 6.1 innings in a start against the Chicago Cubs, as he had a no-decision in a 4-3 loss at Wrigley Field.

During the next two seasons, Singer saw very little action with the Dodgers, pitching five innings in five games, as he spent most of his time in the minor leagues.

The statistic was made official in 1969, and Singer recorded his on April 7, when he took over from Don Drysdale and secured a 3-2 victory over the Cincinnati Reds at Crosley Field.

After contracting hepatitis early in the season, he made a comeback, being named the NL Player of the Month for July as he had a 5-0 record with a 1.84 ERA.

On November 28, 1972, the Dodgers traded Singer, Billy Grabarkewitz, Frank Robinson, Mike Strahler, and Bobby Valentine to the California Angels for Ken McMullen and Andy Messersmith .

He was dealt along with Roy Smalley III, Mike Cubbage, Jim Gideon and $250,000 from the Rangers to the Minnesota Twins for Bert Blyleven and Danny Thompson on June 1.

He was nearly traded for Ron Guidry in a transaction approved by the Yankees but vetoed by Blue Jays president Peter Bavasi.

[3] Singer started the Blue Jays' first spring training game on March 11, 1977 at Grant Field in Dunedin, Florida.

He gave up 11 hits and 3 walks in 4.1 innings, and garnered a no-decision in Toronto's 9-5 win over the Chicago White Sox on a snowy afternoon at Exhibition Stadium.

After retirement he held various scouting and consulting positions with Florida Marlins, Pittsburgh Pirates, Los Angeles Dodgers, and the New York Mets.