The 23-year-old winger, who can also play down the middle, spent the last three-and-a-half seasons with the Magpies.
A regular goalscorer during his time at Chorley, Stephenson netted 21 goals in all competitions for the club last season.
Born in Jamaica, he began his football career coming through the Academy system at Bradford City and made his first-team debut for the Bantams shortly after his 18th birthday.
Stephenson also had a spell with Southport and has been attracting interest from Football League clubs.
Manager Gary Brabin is delighted that he has decided to join Rovers. He said: “I’m really pleased to bring Darren to the Club. He is a player that I have monitored for a number of years.
“I’ve seen his progression over the years and if he can continue that development, he will be a real asset to the club.
“He is quick, hard-working, has good quality on the ball and an eye for goal so I think he’s an excellent addition to our squad.
“The strategy over the summer has been to add firepower to the stability provided by the core of the squad which we have kept from last season and I think we have made some excellent additions.
“We have brought in Darren at the age of 23, Connor Jennings aged 24 and Andy Cook who is 25, to go alongside the exciting attacking players we already have at the club.
“Next season, we will have great attacking options, and all of whom are coming into the peak years of their careers, so we’re all looking forward to the new campaign”.