Bravo missed Chile's 2-1 loss to Paraguay and 0-0 draw with Bolivia last month due to personal problems, while Valdivia has not been selected since November last year, reported Xinhua.
"I am confident in the players that I have at my disposal," Chile coach Juan Antonio Pizzi told a news conference on Tuesday, adding that his side "are going to be well-prepared for these matches".
The Chile team, nicknamed La Roja by their fans, will meet Ecuador in Quito on October 6, before hosting Peru in Santiago five days later.
Despite having won its second Copa America in as many years in June, Chile is currently only seventh in the 10-team South American zone standings.
The top four teams at the end of the two-year qualifying tournament will secure automatic berths at the 2018 World Cup in Russia. The firth-ranked side will earn a playoff spot.
Chile squad:
Goalkeeper: Claudio Bravo (Manchester City)
Defenders: Mauricio Isla (Cagliari), Igor Lichnovsky (Valladolid), Eugenio Mena (Sao Paulo), Paulo Diaz (San Lorenzo), Enzo Roco (Cruz Azul), Erick Pulgar (Bologna), Miiko Albornoz (Hannover)
Midfielders: Arturo Vidal (Bayern Munich), Felipe Gutierrez (Real Betis), Charles Aranguiz (Bayer Leverkusen), Marcelo Diaz (Celta Vigo), Pedro Pablo Hernandez (Celta Vigo), Francisco Silva (Cruz Azul), Jorge Valdivia (Al-Wahda)
Forwards: Alexis Sanchez (Arsenal), Mauricio Pinilla (Atalanta United), Edson Puch (Necaxa), Eduardo Vargas (TSG 1899 Hoffenheim), Junior Fernandes (Dinamo Zagreb).
