It will see Castore become the club’s new on and off-field partner, from the start of the new season later this year, suggesting Mike Ashley’s ownership is coming closer to ending.
The deal with Newcastle follows similar agreements with Rangers FC and Wolverhampton Wanderers FC as Castore continues to disrupt a market dominated by a handful of global brands. It also signed up Saracens rugby club last month.
Castore will supply new designs for home, away and training kits for next season with, for the first time, fans able to buy the same quality Castore shirts that the players will be wearing.
The retailer will also take over the day-to-day running of the club’s e-commerce operations, redesigning the club’s online store, and launching a much wider range of merchandise than previously available to Magpies supporters.
The move is expected to be seen by fans as another indication that Mr Ashley is poised to exit the club.
His Sports Direct stores currently run the club shop at the stadium, which carries the chain’s name, and Sports Direct sells replica shirts in store.
Sports Direct does not stock Castore products and is not expected to.
Castore is also opening a stand-alone store in Newcastle later this month for fans who cannot get to the ground.
Tom Beahon, co-founder of Castore, said: “Newcastle United has a huge and deeply passionate fan base, and we look forward to giving the Toon Army something else to get excited about next season.
“We believe the partnership signals not only a new shirt for the new season but also a new start … for this iconic club.”
Newcastle United managing director Lee Charnley said: “Castore has already built a reputation as an aspirational brand in a highly competitive sportswear market and we feel they are a great partner for the club.”
Castore was launched in 2015 by Mr Beahon and his brother Phil, and has the backing of Sir Andy, New Look founder Tom Singh and Net-a-Porter founder Arnaud Massenet.
It also recently signed up its biggest new investors – billionaire brothers Mohsin and Zuber Issa, the new owners of Asda supermarket.
The premise behind Castore is to develop products using patented fabrics and advanced technical engineering for gym use, athletics, tennis and golf – with an eye to taking on global giants Adidas and Nike.
Castore already has partnerships with a number of leading athletes, including Owen Farrell and Masters-winning golfer Patrick Reed, and recently signed a lucrative partnership with McLaren Formula 1.
The retailer primarily trades online but also has stores in London and Liverpool, and hopes to capitalise on the exercise boost seen during the pandemic and the demand for so-called athleisure clothes.
Revenues are expected to hit £100 million this year and will see the company turn a profit.