The 23-year-old defender has been the subject of fierce interest from the Catalunya club in recent weeks, as they sought to solve their issues at right-back.
Neither Aleix Vidal nor Sergi Roberto managed to stake a regular claim for the post last season, with Barca weakened by the departure of Dani Alves to Juventus.
But after talks with Benfica proved successful, the club announced that Semedo would soon be arriving at Camp Nou.
"FC Barcelona and Benfica have come to an agreement over the signing of Nelson Semedo, subject to the medical tests he will undergo this Friday in Barcelona," a Barca statement affirmed.
The right-back is expected to sign a five-year contract at Camp Nou after an initial fee of €30million was agreed between the clubs.
The Catalans hope to have Semedo travel with the squad next Wednesday for their pre-season tour of the United States.
Barca reportedly turned to Semedo after being rebuffed by Arsenal in their pursuit of Hector Bellerin, with a new right-back having been designated one of their priorities for next season.
The Portugal international is new coach Ernesto Valverde's third signing of the transfer window, following the arrivals of Gerard Deulofeu and young centre-back Marlon.
President Josep Maria Bartomeu stated this week that they hope to complete "two or three" deals before the window closes next month.