After making selected outings in Moto3 in the early part of last decade, Mathias has been regularly racing in World Supersport since 2014, with the highlight being his title glory in '17 with the GRT Yamaha team.
After losing the following year's title to teammate Sando Cortese, the French rider moved to Puccetti Supersport team in 2019 and has since enjoyed two race winning campaigns with the squad and currently sits second in the championship with just the Estoril finale to run.
Puccetti has now decided to give Mahias his WSBK break in 2021 in place of Fores, who announced last week that he would be splitting with the squad after just one year.
Fores previously raced in WSBK Barni Ducati between 2016-18, but was asked to make way for Michael Ruben Rinaldi and spent a year on the sidelines before securing a seat with the Puccetti team for 2020.
"I'm excited to be able to compete in WorldSBK," Mathias said "That was always my goal, and to move up with the Kawasaki and Puccetti Racing is absolutely fantastic.
"I've competed in two Superbike races in the past and have ridden a 1000 in Superstock and in World Endurance, but I know that the ZX-10RR is a very powerful and competitive bike, and I can't wait to get on it.
"I had two aims in my sporting career, the first was to become WorldSSP champion and the second is to win the Superbike World Championship.
"Having achieved the first, I'll now do everything I can to obtain the second too. I know it's a very tough championship, but I'll have a great team and a competitive bike on my side. I want to thank Manuel Puccetti and Kawasaki for this amazing opportunity."
The one-bike Puccetti outfit has endured a difficult 2020 season so far, with Fores able to break inside the top 10 only twice in the opening seven rounds.
Puccetti's results are in contrast to its highs of last year when now factory Yamaha rider Toprak Razgatlioglu scored two wins and 10 other podium finishes to help it score the independent teams' title.
"I'm pleased to announce that we have decided to promote Lucas Mahias from Supersport to Superbike next year," Puccetti said.
"Supporting our riders from the Stock or Supersport classes right up to the top class is part of our team's DNA and is something we have previously done with riders like Franco Morbidelli, Michael Ruben Rinaldi, Randy Krummenacher and Toprak Razgatlioglu.
"I'm convinced that Mahias is a real talent, a solid rider who is always highly motivated. Racing in Superbike has always been his dream and so I'm sure he'll put in maximum effort to achieve the best results.
"On our side, we'll do all we can to help him adapt to the new bike and the new category, without applying any pressure. As soon as we have a 2021 calendar, we'll schedule some tests so that we're prepared for the new season."