Dressed in yellow party T-shirts they sang liberation songs as they alighted from buses, and danced while filing into the conference hall.
The conference will elect a new provincial leadership.
Deputy President Cyril Ramaphosa was expected to open the conference.
More than 400 branches were expected to attend.
“The provincial conference will be attended by 406 branches in good standing which represent 89 percent of branches in Gauteng,” secretary Boyce Manali said on Tuesday.
“All our five ANC regions, including the leagues, held successful councils in line with the conference guidelines.”
Current chairman Paul Mashatile looked set to retain his position with premier David Makhura as his deputy.
Other nominees for the top five positions are health MEC Hope Papo for provincial secretary, former deputy health minister Gwen Ramokgopa as his deputy, and Gauteng legislature speaker Ntombi Mekgwe for treasurer.
The province lost 10 percent of its support in the May general election.