Background Men who have sex with men (MSM) and transgender women (TGW) are at risk for sexually transmitted infections (STIs), including those of the oropharynx. We estimated the prevalence and factors associated with oral sex practices and characterized oropharyngeal STIs among a cohort of MSM and TGW in Nigeria. Methods From 2013 to 2018, TRUST/RV368 recruited MSM and TGW into HIV/STI diagnosis and treatment at community-based clinics in Nigeria. Participants who completed HIV testing and oral sex questions at enrollment were selected. Cross-sectional analyses with bivariate and multivariable logistic regression models estimated odds ratios (ORs) and 95% confidence intervals (CIs). Oropharyngeal swab testing for Neisseria gonorrhoeae (NG) and Chlamydia trachomatis (CT) began in 2014 and for those with diagnostic results at enrollment, the unadjusted association of oral sex practices with oropharyngeal STIs was conducted. Results A total of 1342 participants had a median age of 25 years (interquartile range: 22-29), 58% were living with HIV, and 69% reported oral sex practices. Factors associated with increased odds of engaging in oral sex included living with HIV (adjusted [a]OR: 1.4, 95% CI: 1.1-1.8), self-identifying as a woman (aOR:1.8, 95% CI: 1.1-2.8), mobile phone ownership (aOR:2.3, 95% CI: 1.3-3.9), receptive anal sex (aOR:1.7, 95% CI:1.3-2.3) and multiple male sexual partners (2 to 4 vs. [less than or equal to]1, aOR:1.5, 95% CI: 1.0-2.2; 5+ vs [less than or equal to]1, aOR:2.9, 95% CI:1.9-4.3). Oropharyngeal STI prevalence was 7% (52/752) and higher among those who engaged in oral sex compared to those who did not (unadjusted OR: 2.5, 95% CI:1.2-5.3). Conclusions Oral sex was common and associated with an increased odds of oropharyngeal STIs among MSM and TGW from Nigeria. In the absence of screening and treatment guidelines, condoms continue to be the mainstay for oral STI prevention. A pre-exposure prophylaxis for bacterial STIs would complement current prevention strategies to curb transmission.