Conmebol has joined the major federations that backed Infantino, with Europe and Central America already backing him.
Infantino became frontrunner in the Fifa presidency race, after he announced his intention in October and Platini dropped out after he was provisionally suspended from all football related activities.
The 45-year-old Swiss has revealed an 11-point manifesto on his website, which pledged to increase the number of teams at World Cup finals to 40 and improve transparency throughout Fifa.
Europe’s Uefa were quick to unanimously back Infantino, with Central America’s Uncaf and now South America’s associations putting him in a position of strength.
A Conmebol statement read: “The Executive Committee of the South American Football Confederation has decided to support the candidacy and the work plan of Mr. Gianni Infantino for the Fifa presidency.”
Infantino will contest the election against Prince Ali bin Al Hussein, Jerome Champagne, Sheikh Salman bin Ibrahim al-Khalifa and Tokyo Sexwale in Zurich on February 26.