Scarlets Head Coach, Nigel Davies congratulated his young charge and said: "This is well-deserved. Jon is ready for international rugby, when he came on against Samoa he did very well; he's had a great season for the Scarlets so far and proved he is a quality player and now understands the role of a 12.
"He has obvious strength and is one of the quickest in our squad, when the power, speed and strength combine, at times he is unstoppable.
"He still has things to work on, but there's no doubt he's benefited from a consistent run of games this season and last and playing on the big stage with Wales will add to that experience."
The facial injury suffered by Tom Shanklin in the victory over Samoa gives Davies his chance with Gatland otherwise reverting to the starting line-up chosen to face New Zealand in the Series opener a fortnight ago.
And in a positional switch Blues centre Jamie Roberts moves to outside centre to accommodate Davies at No 12.
Davies joins his Scarlets Lions colleagues, hooker Matthew Rees and fly-half Stephen Jones who return to the Wales starting line-up this Saturday.
Gatland said: "Jonathan came on at inside centre on Friday (against Samoa) when Tom (Shanklin) was injured and he acquitted himself well. That's his natural position, he plays there for the Scarlets and is comfortable there."
WALES: James Hook; Leigh Halfpenny, Jamie Roberts, Jonathan Davies, Shane Williams; Stephen Jones, Gareth Cooper; Gethin Jenkins, Matthew Rees, Paul James, Alun-Wyn Jones, Luke Charteris, Andy Powell, Martyn Williams, Ryan Jones (Captain)
REPLACEMENTS: Huw Bennett, Duncan Jones, Bradley Davies, Dan Lydiate, Dwayne Peel, Andrew Bishop, Tom James.