The 23-year-old came off the bench in Tuesday's heavy defeat to the Chiefs in Hamilton but will start at full-back in the second Test in Wellington.
George North was ruled out with a severe hamstring tear suffered during the First Test, with Liam Williams moving to the wing.
"I've been asked to do a job on the weekend and hopefully I'll be able to do it," said Patchell.
"It's been a bit of a whirlwind few days, but I'm looking forward to the challenge on the weekend.
"It's a really exciting thing to look forward to and I'm sure Saturday night will be bouncing and it will be a great atmosphere to play in front of."
The young back trained with the Wales squad before their defeat to England, but was not selected by Warren Gatland for the tour.
His two previous Wales' caps came on the 2013 tour to Japan when Robin McBryde and Shaun Edwards took caretaker charge while Gatland led the Lions.
Gatland said: "He was potentially unlucky not to be on the tour in the first place and we watched him play 15 for the Blues on a number of occasions and we've been impressed with him.
"He's quick, he's got a big boot on him and we think he can do a job for us.
"He brings a physical element, he's an intelligent rugby player and he's pretty excited about the opportunity."
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