The incident took place last night and the accused has been identified as Dilip Sisodia, a lawyer, who is a resident of Krishna Nagar, police said.
Sisodia, who had called the victim and her husband here from Agra in connection with a case in which he was representing them, was visiting the couple at their guest house in Dampier Nagar area last night, they said.
The accused sent the husband to the market on some pretext, following which he allegedly threatened to kill the woman and raped her at gunpoint.
Kotwali police station incharge, Kunwar Singh Yadav told that the accused has been arrested and an FIR has been lodged on woman's complaint.
Meanwhile, the victim will later be sent for medical tests and for recording her statement before the magistrate.