Shoe manufacturer CCC will take over as the main sponsor of the current BMC team, which is owned by Jim Ochowicz's Continuum Sports company, and Gradek will make the step up from the current CCC-sponsored Pro Continental squad.
"It has been my dream to ride for a WorldTour team and now this dream is coming true," the 28-year-old Polish rider said in a press release.
"To compete at the highest level of racing, and with the best riders, is what I have always wanted to do, so I'm very excited and I can't wait for the upcoming season.
"To be be part of any WorldTour team would be wonderful, but to be part of a Polish WorldTour team will be very special.
"I know that I can learn a lot from the experienced riders in the team, and I definitely want to develop more as a cyclist, and to be helpful to my teammates," continued Gradek, who rode for the British ONE Pro Cycling Continental team in 2017.
"I'll do my best and believe I'll be with the right team to achieve this. I would like to focus on some of the Classics, but I also want to take advantage of the team's experience and expertise to improve my time trials as well."
General manager Jim Ochowicz is engaging a rider whose only two individual pro wins came in 2014, when he took a stage and the overall classification at the Tour of China I.
However, this season Gradek has shown that he is already a key part of any team time trial set-up, helping his team to fifth on a stage of the Volta a la Comunitat Valenciana, to second place in the team time trial at the Settimana Internazionale Coppi e Bartali, and to first place in the discipline at a stage of the Sibiu Cycling Tour in July.
He also rode to ninth place at the Worlds TTT with the Polish national team.
"Kamil has a lot to learn and will gain valuable experience when he makes the transition to the WorldTour level," Ochowicz said. "He'll be a valuable domestique, and we hope he can take opportunities for himself as he continues his development.
"Kamil has also shown potential in the Classics with 10th at Nokere Koerse this year, and although he'll be making his debut with a WorldTour team, he's already raced some of the WorldTour one-day races, including the Cyclassics Hamburg and the Rund um den Finanzplatz Eschborn-Frankfurt. We look forward to seeing what Kamil can do with this opportunity next season."