Kubica and Deletraz both make the move across from the Prema squad, joining WRT's previously-announced silver-rated driver Rui Andrade at the wheel of the Belgian team's #41 Oreca 07-Gibson.
Sean Gelael is so far the only driver named for the #31 WRT entry.
Kubica contested his first full season in sportscar racing for WRT in 2021 in the European Le Mans Series, winning that year's title alongside Deletraz and Yifei Ye.
He and Deletraz joined Prema for the Italian squad's debut in the WEC last year, sharing a car with Lorenzo Colombo, but will now return to the WRT fold for the upcoming season that kicks off at Sebring in March.
Kubica's personal sponsor Orlen also switches its allegiance from Prema to WRT for 2023.
"I am very happy to be back in the WRT family and to be representing Orlen Team WRT, but this time in WEC, as we raced together and won the ELMS championship in car #41," said Kubica.
"It will be my third year with Louis, but my first with Rui, who I know well from the paddock and Louis has always spoken very highly of him from their time in IMSA together.
"It will be a big challenge to race in the WEC and of course at Le Mans, it would be nice to get one more lap this time, which we missed in 2021 when we lost the win in the last lap. We will stay focused, and we will work hard to achieve the best results possible!”
Deletraz adds another full season in the WEC to his previously-announced ELMS programme with Racing Team Turkey and his IMSA Endurance Cup deal with Acura squad Wayne Taylor Racing.
Andrade meanwhile stays on at WRT for a second season in the WEC after sharing a car last year with Norman Nato and Ferdinand Habsburg, winning a race at Monza.
WRT boss Vincent Vosse said: "I’m so pleased that we get to work with drivers who we know very well.
"Louis and Robert were a fundamental part of our 2021 successes, where they became ELMS champions in our first season with the LMP2, and we all remember the dramatic last lap at Le Mans, which showed just how competitive they are together!
"It’s great to see them teamed up with Rui, we are going for a maximum attack strategy with our line ups in the 2023 season.”
