Condoms have been and are still an important part of HIV preventative measures worldwide, and many countries have designed programmes that encourage their use. Consistent and correct condom use among HIV-positive individuals is important in preventing multiple infections. Hence, the uptake and determining factors associated with condom use were investigated in this study. This study was aimed at determining the level of, and factors associated with, condom use among HIV-positive postnatal women in primary health care facilities in Tshwane sub-district 1, Gauteng Province, South Africa. A descriptive cross-sectional study was conducted among 326 HIV-positive postnatal women aged between 15 and 50 years who were conveniently selected and voluntarily participated in the study. A self-developed pretested questionnaire was used to collect data on level of condom use and factors associated with its use from the selected participants. Statistical tests of correlation were then used to determine the association between frequency of condom use during sexual encounter and condom use at last sexual encounter with the independent variables. Regular condom use during sexual encounters was reported by 63.2% of the participants while 83% of the participants reported using a condom at their last sexual encounter. Frequency of condom use during sexual encounter was found to be associated with employment status (p < 0.05), residence (p < 0.001), number of children (p < 0.05), first HIV diagnosis (p < 0.05) and disclosure of HIV status to partner (p < 0.05). Condom use at last sexual encounter was also found to have a significant statistical association with level of education (p < 0.05) and the ability to negotiate condom use (p < 0.001). A good proportion of the participants used condoms regularly. Interventions to improve condom use among this population should focus on female empowerment by investing in their education, and economic empowerment to improve their economic status, which, in turn, would help the women to better negotiate condom use. The other factors mentioned above should also be considered when developing health education policies and programmes about condom use amongst HIV-positive postnatal women.