Parkin's original contract was due to expire next summer, and Parkin had been linked with moves away from the County Ground to clubs including Southampton.
Parkin should be pen to paper before the QPR home game this weekend, which will increase his value should another club try to bid for him.
Parkin, 22, joined Swindon in the summer of 2001 and since then has scored over 30 league goals for Swindon including the only goal of the game in last weekend's 1-0 win over Oldham.