Cuevas trained with the Stamford Bridge club on a trial basis in 2012, and a transfer that will see the midfielder move permanently from O'Higgins has reportedly been agreed.
With Cuevas likely to play for his country at this summer's Under-20 World Cup in Turkey, the youngster expects to join up with the Chelsea squad around the start of pre-season training.
Having impressed at the South American Under-20 championships in January, Cuevas' stock rose among top European clubs and Chelsea have now made their move to get his signature.
"I'm very happy," Cuevas told El Tipografo. "This week everything was finalised and I'll join in the middle of the year.
"Chelsea were following me for more than a year. What I wanted happened, which was joining this club.
"The Under 20 World Cup will come in the middle of the year and I hope to be in the squad and play some minutes as I really want to. If I play the World Cup, I'll then go to England. Otherwise I'll go there in June."