Wilson Chowdry, from the British Pakistani Christian Association, was speaking after authorities in the country hung Mumtaz Qadri - a man on death row for the murder of the late politician Salman Taseer.
Mumtaz Qadri murdered Salman Taseer because he was outspoken against Pakistan's blasphemy laws, which are used to target Christians and other minorities. He was his bodyguard at the time.
Mr Taseer had also called for Asia Bibi, a Christian woman currently sentenced to death for insulting the Prophet Muhammad, to be pardoned.
Officials report Qadri, who was a hailed as a hero for his action by some Islamists, was executed at Adiala jail in Rawalpindi at 4.30am today (local time).
MumtazQadri being hanged is a victory to #Pakistan. NOT the #Taseer family.The safe return of my brother is the only victory my family wants
— Shehryar Taseer (@shehryar_taseer) 29 February 2016
Qadri said it was his religious obligation to kill Salman Taseer and news of Qadri's death has prompted street protests.
Salman Taseer's son, Shahbaz Taseer, was abducted in Lahore in August 2011 and his location is currently unknown.
Four months after Salman Taseer's death, Pakistan's only Christian cabinet member, Shahbaz Bhatti, was also assassinated.
Wilson Chowdry told Premier: "This has been a very brave move. I do commend the Pakistani government.
"Whatever people feel about death sentences the fact is it is part of Pakistani law, and now they have actually practised an act of punishing a man guilty of extremism in their country.
"The Supreme Court, when they made the judgement Qadri, openly said the blasphemy laws should not be above reproach. That opens the door for the blasphemy laws now to be reanalysed.
"This legacy of his killer being killed is now another watershed moment in what I believe will be the eventual turnaround of humanitarian rights in Pakistan."
Listen to Premier's Aaron James speaking to Wilson Chowdry: