Since retiring from international cricket in 2013, the 42-year-old has coached extensively around the world, including stints as the batting coach of Bangladesh and Sri Lanka, along with his role as fielding coach of the Kolkata Knight Riders in the 2018 IPL.
Boasting an impressive playing record, Samaraweera scored 14 Test centuries in his 81-match career, two of which were made against New Zealand on the tour of Sri Lanka in 2009, ending with an average of 48.76 and a top score of 231 against Pakistan in Karachi.
Blackcaps coach Gary Stead said Samaraweera would bring great experience and skills to the group.
“We're delighted to welcome Thilan into our environment for the Test phase of the tour. His knowledge of Sri Lankan conditions will be invaluable and he'll offer great assistance to Peter Fulton on his first tour,” Stead said.
“Having an extra support coach worked really well for us at the World Cup where we had Luke Ronchi on board, and we're sure Thilan will also offer a lot to the group,” he added.
Samaraweera will join with the Test squad on arrival in Colombo this week.
New Zealand will play against Sri Lanka in two Tests to begin their World Test Championship campaign at Galle on August 14.