The experienced 33-year-old joins Saints on a one-year deal from Aviva Premiership rivals Wasps. Haskell was a member of the Lions squad which toured New Zealand in 2017 and has also represented England 77 times, including at two Rugby World Cups.
“I’m really excited and humbled to be joining a giant of English rugby in Northampton Saints,” Haskell told Saints’ website.
“Having had the opportunity to play against them for many years now, I know this is a club with a proud history and a set of passionate and loyal supporters who always make their presence felt.
“It’s no secret that I want to continue my international career for as long as possible; the only way I can do that is by putting my best foot forward in club rugby and helping Saints fight their way back into contention for silverware.
“There’s a real buzz around Franklin’s Gardens at the moment with the arrival of (director of rugby) Chris Boyd, a new coaching team being put in place and a number of top-quality players also joining the squad. I can’t wait to get started in black, green and gold.”
Haskell made more than 200 appearances for Wasps during two spells, winning both the Premiership and Heineken Cup.
The 6’ 4” player, who has also spent time with Stade Francais, Japanese club Ricoh Black Rams, and New Zealand side Highlanders, can play in any of the three positions across the back-row.
He becomes Saints’ seventh signing ahead of the 2018/19 season.
Northampton’s director of rugby Boyd said: “We’re thrilled to have captured James’ signature for next season as he’s a player that can bring so much to Saints.
“Not only is he a superb leader with bags of experience at the very highest level, but James is clearly still extremely hungry to win trophies in club and international rugby.
“His record speaks for itself and I have no doubt that he will be an excellent fit for Northampton, both in the side and within the club.”
The 30-year-old’s contract with Wasps expires at the end of the season and he has decided to remain in England as he seeks to resurrect his international career.
The Cherry and Whites, who have also signed winger Matt Banahan from Bath ahead of next season, finished seventh in the Aviva Premiership this season and were beaten finalists in the European Challenge Cup.
Cipriani had received offers from France and Japan but to remain eligible for England he needed to stay in the country.
His arrival at Kingsholm will give options to head coach Johan Ackermann with Billy Burns and Owen Williams vying for the number 10 jersey, although Williams can be utilised at inside centre.
Cipriani will also get the chance on the big stage in Europe with Gloucester’s Challenge Cup final appearance earning them a place in the Champions Cup next season by virtue of opponents Cardiff Blues already qualifying through the PRO14.
Cipriani’s replacement at Wasps has already been announced with the capture of New Zealand fly-half Lima Sopoaga.
He will sign off his Wasps career with a play-off campaign as Dai Young’s side face Saracens in the semi-final on Saturday, hoping to advance to a final against Exeter or Newcastle.
It may have been a gutsy victory in the end, but nevertheless, Leinster are deserved European champions for a fourth time in ten years after an impressive unbeaten campaign.
It’s rare for any team to go through the pool and knock-out stages unbeaten but Leinster emulated Saracens in 2016 by becoming the second club to achieve this feat.
Despite being drawn in a tough pool they managed to advance with a 100 percent record from their six matches, before going on to beat 2017 champions Saracens in the quarter-finals and PRO14 winners Scarlets in the semi-finals.
For a team to do this not only takes a serious level of consistency, but also requires remarkable squad depth, an efficient game plan and a well-structured training schedule that allows players to rest in order to be fresh and injury-free for a gruelling eight-month season.
The Bilbao rain may have forced the final against Racing 92 to be a scrappy affair at times, but the strength of both defences was a testament to both sets of coaches.
In the build up to the match, much talk centered on whether Racing could contend with Leinster in a high-tempo game for 80 minutes, but to their credit they were superb, with Teddy Iribaren and European Player of the Year Leone Nakarawa shining throughout.
Iribaren, in particular, had the biggest job of all when stepping into the coveted nine shirt that the injured Maxime Machenaud had thrived in all season before suffering a knee injury three weeks ago.
The 27-year-old controlled the game with aplomb, with his clever box kicking pinning Leinster back deep in their own territory all afternoon.
Even in the dying minutes, with three points separating the sides, they pressed hard with discipline and accuracy to try and force the game to extra-time, only for Remi Tales to see his snap drop-goal attempt drift wide.
Still, Racing can walk away from this final – although disappointed – but with pride and confidence in their ability and still a Top14 title to battle for when they play in the semi-finals on May 26.
But for the Irish side, their remarkable year shows no sign of ending. They may not have performed to their stellar ability, but to become only the second team in history to win four European cups is remarkable and rich credit to all the coaching coach at the Dublin club.
With star men Dan Leavy (23), James Ryan (21), Gary Ringrose (23), Robbie Henshaw (24), Jordan Larmour (20), Luke McGrath (25) and Tadhg Furlong (25) all pivotal to the victorious campaign, Leinster possess enough youthful talent to dominate for years to come.
From 1-22, there are endless stars in this Leinster side, but one of the shining lights from Bilbao was man-of-the-match James Ryan.
At just 21, the Dublin native is yet to lose a professional game in his 21 outings for club and country, but aside from that, he is already one of the best players in the world at the moment.
His voracious workrate makes him one of the central figures in the Leinster pack, coupled with his ability to pass and make breaks, which is a testament to the 15-man game Leinster are implementing.
His stats from northern Spain were outstanding, with 11 carries and 12 tackles, with so many of them being the tipping point that makes a difference in gripping, Test level environment.
Behind him, back-rower Dan Leavy continues to purr with dominance and was also in the running for man-of-the-match.
The 23-year-old has emerged as one of the key figures in this Leinster side this season, with his battered face exemplifying the effort he puts in, and his effective carrying and tackling ability makes him an extraordinary presence for any side.
The loss of captain Isa Nacewa will be a blow at the end of the season, but to finish his Leinster career with another European title and potentially a league crown will be a fitting way to bow out.
And the legendary skipper, who will retire from the game at the end of this month, invited Ulster-bound Jordi Murphy to lift the cup with him – a fitting note to another player who has been instrumental to Leinster’s success over the last number of seasons.
With such a rich vein of young talent adding to the experience of chief lieutenants Johnny Sexton and Rob Kearney, Leinster have a serious balance to continue winning for the foreseeable future.
Business resumes today when they return to training to look ahead to Saturday’s PRO14 semi-final against Munster, but the legacy created and the squad adds to reason why four European trophies can’t become five.