Ram Kumar Chowdhary took oath as legislator from Doon on Thursday after permission from a court in Panchkula near Chandigarh. He was brought to Shimla from Ambala jail under heavy security.
Mr Chowdhary is the main suspect in the murder of a 24-year-old Dalit woman in Panchkula on November 22 last year. But he insists he is innocent.
"My opponents framed me in this conspiracy. I have full confidence in the judiciary and will be proved innocent," he said.
"I will continue to work as a legislator. I have just submitted a list of my priorities as a legislator to the Assembly Speaker," he said.
The Dalit woman was found murdered in Sector 21 of Panchkula. The police were clueless for over a month, but phone call records are believed to have led them to Mr Chaudhary.
The Congress has suspended the politician, but the BJP says he should not be allowed into the Assembly. BJP leader and former chief minister Prem Kumar Dhumal said: "This case is shameful not only for Himachal but the entire country."
Buti Ram, the murdered woman's father, said the legislator had no right to be in politics and demanded action against him.
But Assembly Speaker BB Butail defended the oath-taking, saying Mr Chaudhary had not been convicted yet. "Ram Kumar Chaudhary got the court's permission to be sworn in. The case against him is under investigation. When its findings are out, we will see what is to be done."
(With inputs from PTI)