The 26-year-old midfielder, who made 36 appearances as Vale clinched promotion to League One last season, will now stay with the club until the summer of 2014.
"Doug has made a telling contribution to the squad during his time at Port Vale, both on and off the pitch, and I'm pleased he has decided to sign a new deal with us," manager Micky Adams told the club's official website.
"Sometimes these things take time and it needs to be right for both parties. Doug was always a part of our plans and I'm looking forward to working with him for a further season."
Loft added: "It was never in doubt that I wanted to stay with the club, especially after being part of the side which won promotion last season.
"We have all been working hard in pre-season since reporting back last week and I know that everyone is looking forward to the season ahead."