Antiretroviral therapy (ART) coverage among HIV-infected tuberculosis (HIV-TB) patients has been suboptimal in Myanmar and the reasons are unknown. We aimed to assess the ART uptake among HIV-TB patients in public health facilities of Ayeyawady Region from July 2017–June 2018 and explore the barriers for non-initiation of ART. We conducted an explanatory mixed-methods study with a quantitative component (cohort analysis of secondary programme data) followed by a descriptive qualitative component (thematic analysis of in-depth interviews of 22 providers and five patients). Among 12,447 TB patients, 11,057 (89%) were HIV-tested and 627 (5.7%) were HIV-positive. Of 627 HIV-TB patients, 446 (71%) received ART during TB treatment (86 started on ART prior to TB treatment and rest started after TB treatment). Among the 181 patients not started on ART, 60 (33%) died and 41 (23%) were lost-to-follow-up. Patient-related barriers included geographic and economic constraints, poor awareness, denial of HIV status, and fear of adverse drug effects. The health system barriers included limited human resource, provision of ART on ‘fixed’ days only, weaknesses in counselling, referral and feedback mechanism, and clinicians’ reluctance to start ART early due to concerns about immune reconstitution inflammatory syndrome. We urge the national TB and HIV programs to take immediate actions to improve the ART uptake.