Dalbir Kaur, the sister of Sarabjit Singh, who died in a Pakistan jail in 2013 on Sunday joined the Bharatiya Janata Party (BJP).
"She joined the party in the presence of BJP MLA and Punjab Minister Surjit Jyani at a conference organised by the party's Kisan Morcha here," Punjab BJP Kisan Morcha general secretary Gurwinder Singh said.
When asked by reporters, Kaur confirmed that she had joined the BJP.
Kaur had grown close to the BJP even in 2005, during her struggle to get her brother out of jail, and there were reports of her joining the party.
Sarabjit died following an attack on him by inmates of a Lahore prison in April 2013.
He was convicted for terrorism and spying by a Pakistani court and sentenced to death in 1991. However, the government stayed his execution for an indefinite period in 2008.
Meanwhile, Union Home Minister Rajnath Singh could not attend the Kisan Morcha's conference because of inclement weather.