But the 25-year-old feels the time is right for a move that he hopes will help him achieve his aim of becoming an England regular at Test and one-day level.
Willey, who had a year to run on his Northants deal, has signed a three-year deal at Yorkshire and will join at the end of the current campaign.
The academy graduate has established himself as one of the top 20-over and 50-over players in the country since rising through the Northants ranks.
The son of former England all-rounder Peter Willey, Northampton-born David inspired his county to a memorable T20 success in 2013, taking a hat-trick in the final against Surrey.
And just last week he smashed a stunning 100 from 40 balls to help the Steelbacks beat Sussex Sharks and progress to finals day on August 29.
But Willey has decided he must move on to realise his ambitions in the game.
And he said: “I am really excited to be joining Yorkshire and being part of a progressive side,” said Willey, who made his first-class debut in 2009.
“I’m looking forward to working with Jason Gillespie and the rest of the Yorkshire lads.
“This has been a tough decision to make because of my personal attachment to the County Ground. I came here many, many times as a boy and dreamed of playing for Northants.
“I will always be grateful for the years of coaching and mentoring that I have received which gave me the best start to my career.
“However, I feel that the time is right to move on, to experience a new approach to training and to broaden my cricket education.
“Yorkshire gives me the best opportunity to challenge myself working alongside some of the best players in the country.
“I would like to take this opportunity to thank all of the staff and fans of Northants Cricket for their incredible support.
“I don’t believe I would have achieved this much had it not been for the opportunities that Northants has given me.”