The left-back, who spent last season on loan at Benfica, is set to sign a four-year contract with the Liga champions.
"Atletico Madrid and Granada have reached an agreement for the transfer Guilherme Siqueira, pending a medical and the signing of contract by the player," a statement on the Rojiblancos' official website read.
It is believed that Siqueira has been signed as a replacement for Atletico's current left-back Filipe Luis, who is reportedly close to joining Chelsea.
However, sporting director Jose Luis Caminero would only say that the Brazilian, who is expected to cost the club €10 million (£8.1m), will prove an excellent addition to Diego Simeone's squad.
"He increases the internal competitiveness of the group, which is what we always look for from the players who come to our club," he stated.
"He's a very good player at set pieces, a penalty taker, very offensive but with great defensive virtues and excellent positioning. "