The 25-year-old, whose two previous caps came against Egypt and Gabon, was named in the Selecao's squad for friendlies against Honduras and Chile in Miami and Toronto in mid-November.
The former Anzhi Makhachkala player, who moved to Stamford Bridge in August, has a chance to impress former Blues coach Phil Scolari, now in charge of Brazil, as he assesses his options ahead of next year's World Cup.
"I was always with expectation, hopeful, waiting for an opportunity," he told UOL. "Thank God it happened at this time and I was very happy."
Willian's fellow Brazilians at Chelsea - David Luiz, Oscar and Ramires - were delighted to hear that their club team-mate had earned his national call-up papers.
"They became very happy when I was called up, they came over, hugged me, told me that this was a happy moment and that I deserved it," added the Samba star.
"We had never really talked much about the national team, we only did after I was called up. Then I started asking what it is like, what Scolari is like, they said a lot of good things about him and about the environment there. They gave me good tips for when I arrive there."
Reflecting on his first few months with the west London club, Willian called Chelsea, "a wonderful club, and I am very happy."