Willey has signed a four-year deal at Wantage Road, and returns to the club where he began his career before leaving for Headingley at the end of the 2015 season.
“The best journey takes you home,” said Willey, whose father Peter also played for the County and England.
“Wantage Road is home. I grew up playing on the outfield, behind the stands and in the groundsman’s shed.
“When I think back to my first introduction to cricket, I think of Northants.”
And he added: “Northants supported and nurtured me in my younger years and gave me the opportunities to achieve my childhood dreams.
“During the seven years I’ve been away, I have continued to watch the club closely and found myself celebrating their successes.
"I always hoped at some stage in my career I would find my way back and I’m excited that the time is now.”
Willey, who is the white-ball captain at Yorkshire this season, is still very much an England player and this week jets off to the Netherlands to take part in the ODI series against the Netherlands.
“My love and passion for Northamptonshire has always been there and I hope I can give the club more than just my runs and wickets," said the 32-year-old, who went to Northampton School for Boys, and played cricket for the Old Northamptonians as a youngster.
“I still have great ambitions in the game, to play at the highest level, to win trophies but also to give back to the club that has given me so much.”
An accurate left-arm swing and seam bowler and explosive batsman, Willey made 197 appearances for Northants between 2009 and 2015.
A graduate of club’s junior pathway, Willey has scored more than 4,000 runs and taken more than 250 wickets across all formats for Northamptonshire.
He was part of the Steelbacks team that won the T20 Blast in 2013, hammering a brutal half-century and also taking a hat-trick in the memorable final win over Surrey, and he was also in the team that finished runners-up in 2015.
Willey sits in the county’s top 10 runscorers and second in the Steelbacks all time wicket takers list. The left-hander was recently chosen by supporters as Northamptonshire’s greatest ever T20 player.
For England, Willey has made played 52 one day internationals, taking 69 wickets at 31.6 apiece at an economy rate of 5.67, with best figures of five for 30. He has also scored 377 runs at 23.56, with a top score of 51.
He has also played in 32 T20 internationals for his country, claiming 38 wickets at 22.47 apiece at a strike-rate of a wicket every 16.8 balls.
His signing is a massive coup for the County, and chief executive Ray Payne is understandably delighted.
“It’s brilliant to be able to confirm the signing of David Willey and to bring him back to Northamptonshire,” he said.
“It’s a significant move that makes our ambitions for the professional squad really clear.
“We’ve already seen what he’s able to do for the Steelbacks and the international experience David has gained in white ball cricket further strengthens our squad and really supports our goals of bringing more trophies at Wantage Road.”