Sousa returned to the Davis Cup in September to help Portugal defeat Belarus and gain promotion to Europe/Africa Zone's Group I in 2016. Despite losing his first singles rubber, he won the doubles rubber with Elias and the deciding singles rubber against Uladzimir Ignatik. At the St. Petersburg Open, Sousa reached his third final of the season. Following wins over Marcel Granollers, Simone Bolelli and Dominic Thiem, Sousa was runner-up to Milos Raonic in three sets. In October, Sousa entered on a 1–4 run with early round losses at the Malaysian Open, the Japan Open, the Shanghai Masters and the Kremlin Cup. At the Valencia Open, Sousa capped the season with his second career ATP title and the first of the season in four final attempts. After beating four higher-ranked players, including Benoît Paire, Sousa defeated 7th seed Roberto Bautista Agut in the final in three sets. He reached a new career-high ranking in the following week at world No. 34. Sousa finished the season at career-high world No. 33 with 38 singles wins. In November, he received the award for Tennis Personality of the Year for the second time from the Portuguese Tennis Federation and the Confederação do Desporto de Portugal.