BBC Sport reports that the 28-year-old will move for a fee of £6.2 million and will act as a replacement for Gael Clichy, who left the Gunners for Manchester City earlier this summer.
Santos has won 22 caps for the Seleção and was Brazil’s first choice left-back at the Copa America. He has been with Fenerbahce since joining from Corinthians in 2009, and has also played for Figueirense, Flamengo and Atletico Mineiro.