The actors have been a part of the brand's India journey since 2014.
Hrithik said in a statement: "I am proud of the brand's growth in India and am very excited to be a part of yet another successful innings of the brand in India in 2016."
Sonam said: "I am pleased to be associated with OPPO which caters to the consumers with exceptional products."
OPPO is a global technology brand dedicated to providing consumers across America, Africa, Europe, Oceania and Asia with its products.
"Both Hrithik and Sonam are youth icons and are looked up to for their style and attitude, which is completely in tune with our brand philosophy, which is about young at heart and pursuing for perfection, and always be a trendsetter," said Sky Li, vice president, OPPO, and managing director of International Mobile Business.