Labour MP Grant Robertson took to Twitter last night, writing: "Struggling to find words for the loss today of two great campaigners for social justice -Peter Williams and Peter Conway. Huge losses. RIP," while Bill Ralston wrote, "Sir Peter Williams QC RIP. A good and generous man gone. Sad."
Writer Hamish Keith called Sir Peter "a very fine man and a great New Zealander," and Mayor Len Brown wrote "Sir Peter Williams QC was a voice for those in need. Unrelenting, fearless. Our thoughts tonight are with his family and friends and all those he worked with."
Nigel Hampton QC said Sir Peter was always warm, welcoming and hospitable.
He said Sir Peter's involvement in prison reform was inspired by the "Victorian" conditions seen in New Zealand jails in the 1950s and 1960s.
"Once we started going into prisons as young lawyers we saw how degrading the conditions were. It made you think to yourself, 'there must be a better way,' and it became a lifelong passion for him."
He said Sir Peter had a charisma about him that gave him the ability to speak to people and evoke sympathy and compassion - which made him a great criminal lawyer, and prison reform advocate.
Mr Hampton said not everyone agreed with his ideas though - and he copped a lot of flak for them.