Marlos, 29, is expected to join the national team's training camp on Monday along with 25 other players.
"This is a very emotional moment. I am extremely happy to become an Ukrainian citizen and get the chance to play for the national team. I need some time to learn the language," Marlos told local TV.
The Ukrainian Football Federation sanctioned Marlos' selection after receiving confirmation from Brazil's football association that he had not played for the South American team.
Ukraine, who are currently fourth in Goup I with 14 points and trail leaders Croatia by two points, will play in Kosovo next Friday before hosting the Croatians Oct. 9.
The group winners automatically qualify for the 2018 World Cup finals in Russia while the second-placed team will be in the running for a playoff spot.
Marlos moved to Ukraine in 2012 to join Metalist Kharkiv and two years later secured a transfer to Shakhtar, scoring 34 goals in 180 games.
(Reporting by Igor Nitsak, editing by Pritha Sarkar)
