Hartley was replaced as Saints captain in 2015 having previously worn the armband for seven years...
Hartley was replaced as Saints captain in 2015 having previously worn the armband for seven years, but the New Zealand-born player has resumed the role from flanker Tom Wood, who led the club to a seventh-placed finish in the league last season.
The hooker -- capped 86 times by England -- has made 229 appearances for Northampton since arriving in 2006 from Worcester Warriors, and was part of the side that won the 2014 Premiership title.
Hartley's previous deal was due to expire at the end of the 2017/18 season, and the length of his new deal has not yet been disclosed by the club.
The 31-year-old, who was a surprise omission from the Lions squad that drew in New Zealand, is delighted yet slightly shocked that he was asked to lead the Saints once again.
"It was an easy decision to commit my long-term playing future to Northampton Saints," Hartley told the club's website.
"When Jim approached me about taking on the captaincy I was surprised. For me the timing is right and it is certainly a challenge I want to take on. I'm very passionate about the Saints and would love to see us competing for trophies. We have some valuable experience within the squad that will be driving the team forward this year."
Northampton director of rugby Jim Mallinder is delighted to hand back captain's responsibilities to his long-serving hooker.
"Dylan has rightly received recognition as a superb captain for club and country," said Mallinder.
"He led the team during a very successful period for us, has the respect of the rest of the squad and coaches alike, and knows what it takes to win silverware."
Hartley -- despite being blighted by disciplinary problems throughout his career -- has led England to back-to-back Six Nations titles.