The 21-year old Haitian international, known as the 'Haitian Xavi', has moved to the MLS outfit after plenty of negotiations between the two clubs.
"It was a long process because his formation rights were owned by Braga," SKC manager Peter Vermes said.
"We got that settled and taken care of so now we have him under contract. I think he has some really good qualities.
"We wouldn't have waited this long to sign him if we didn't [think that]. He can have an impact on this team."
Joseph, who has six senior caps for Haiti, will be added to Sporting's roster pending receipt of his International Transfer Certificate and P1 Visa and he will occupy an international roster spot.