A 2.06m small forward who hails from New York, the maternal grandparents of Harkless hail from the Caribbean country.
"I am grateful for the opportunity to play for the national team of Puerto Rico," Harkless said in a statement issued by the Puerto Rican Basketball Federation.
"I look forward to playing alongside these men and helping win games on an international level.
"It is an added bonus that I get to play for my extended family.
"I hope to make them and the people of Puerto Rico proud."
Puerto Rico first reached out to Harkless when he was a student/athlete at St John's University in New York.
He decided to commit to Puerto Rico during a recent visit from national team coach Paco Olmos, and team manager Alfredo Morales.
"Over the past five months, we have been working with Moe to get him to join the team," said Puerto Rican Basketball Federation President Carlos Beltran.
"I want to recognize the help that our advisor Joel Katz has given us during this process.
"On the one hand, Harkless' addition brings a new dimension to our national team, and, on the other, it can increase the interest of Puerto Rican fans in Orlando."
The plan is for the 20-year-old to travel to Puerto Rico and spend some time on the island after the end of the NBA season.
In additional comments to Primera Hora, Beltran said: "He is eager to come to Puerto Rico and he has already made the compromise to come a week to get to know the country and his family here.
"We are going to do with him what we did with Renaldo Balkman, whom we took everywhere.
"We want him to identify with the country and for the country to identify with him."
Harkless is in his second season in the NBA with Orlando.
"This young man is going to be a star in the future," Beltran said.
"He has all the physical qualities to be one.
"As a person, he is humble and respectful.
"I think now in Orlando, he is going to be more appreciated now that the Boricuas there know that he will play with us.
"There were some that knew it but not all of them.
"Now everyone will know."
Puerto Rico qualified for Spain 2014 when they earned a spot in the Semi-Finals of last year's FIBA Americas Championship in Caracas, Venezuela.
They finished second in the tournament after losing to Mexico in the Final.
The draw for the FIBA Basketball World Cup takes place on Monday at 7pm CET in Barcelona, Spain.