He ran in the 1975 provincial election, and finished second against LiberalVern Singer in Wilson Heights. He was elected to the Ontario legislature in the 1977 provincial election, defeating New Democratic Party candidate Howard Moscoe by 2,993 votes. He served as a backbench supporter of William Davis's government, and defeated Liberal Elinor Caplan to be re-elected in 1981. Rotenberg supported Dennis Timbrell to succeed Davis as party leader and premier in 1985, and endorsed Larry Grossman after Timbrell's elimination on the second ballot. Rotenberg appears in a pictorial section between pages 106 and 107, standing between Grossman and Timbrell as the latter accepts a Grossman button. The caption beneath the picture identifies Rotenberg as a Timbrell supporter. Grossman lost to Frank Miller on the final count. After the leadership convention, Miller appointed Rotenberg to cabinet as a minister without portfolio responsible for Urban Affairs. Near the end of his tenure as premier, Bill Davis announced that he would extend full funding to the province's Catholic school system. Anglican Archbishop Lewis Garnsworthy, a vocal opponent of the plan, responded by charging that Davis had changed Ontario's education system "by decree", in the same way that Adolf Hitler had changed the education system in Nazi Germany. Rotenberg later said that Garnsworthy's comments created a climate of religious intolerance in the province, and took support away from the Progressive Conservative Party. "I think he would probably get the Ian Paisley award of the year, because his speech made it respectable to be anti-Catholic," Rotenberg was quoted as saying. Although the opposition Liberals and New Democratic Party also supported full funding for Catholic schools, the governing Conservatives were more seriously affected because some of their religious supporters abstained from voting, depriving them of significant support. Garnsworthy's speech was credited with prolonging the controversy during the 1985 campaign. Rotenberg was unseated in 1985 campaign, losing to Liberal candidate Monte Kwinter by 2,188 votes. The Progressive Conservatives were reduced to a minority government and it was brought down by a Liberal-NDP accord shortly after the election. A decade later, Rotenberg attempted a return to politics and campaigned for the House of Commons of Canada in the 1997 federal election as a candidate of the Progressive Conservatives in the riding of Eglinton—Lawrence. He lost to incumbent Liberal Joe Volpe. The Canadian Alliance tried to recruit Rotenberg as a candidate in Willowdale for the 2000 federal election, but he was disqualified because he had not been a party member for long enough.
