The young striker has been at Elland Road since he was seven-years-old.
It sees the forward continue his 12-year stay at Leeds, having first arrived as a seven-year-old.
Though Parkin is yet to make an appearance for the first team at Elland Road, he has been regularly involved for the club's Under-21 side over the last 12 months. The striker turned out 27 times last season at that level, netting 9 times as Leeds finished in fourth spot in the Under-21 league.
The 19-year-old was involved with the match day squad earlier this season, with the Leeds site reporting he narrowly missed out on a place on the bench against Fulham.
Parkin turned professional in 2013, and is the latest in a number of talented young United players to have committed to the club in recent days, with Alex Purver agreeing a new deal, and academy stars Frank Mulhern, Tom Lyman and Bailey Peacock-Farrell all signing professional contracts as Leeds prepare for a new era under Uwe Rosler.
Owner Massimo Celino has previously declared that it is his desire for Leeds to field a side full of academy talent, and the club certainly appear to be making use of their youngsters if the recent spate of new contracts are anything to go by.