Background: Despite bearing the largest HIV-related burden, little is known of the Health-Related Quality of Life (HRQoL) among people living with HIV in sub-Saharan Africa. One of the factors contributing to this gap in knowledge is the lack of culturally adapted and validated measures of HRQoL that are relevant for this setting. Aims: We set out to adapt the Functional Assessment of HIV Infection (FAHI) Questionnaire, an HIV-specific measure of HRQoL, and evaluate its internal consistency and validity. Methods: The three phase mixed-methods study took place in a rural setting at the Kenyan Coast. Phase one involved a scoping review to describe the evidence base of the reliability and validity of FAHI as well as the geographical contexts in which it has been administered. Phase two involved in-depth interviews (n = 38) to explore the content validity, and initial piloting for face validation of the adapted FAHI. Phase three was quantitative (n = 103) and evaluated the internal consistency, convergent and construct validities of the adapted interviewer-administered questionnaire. Results: In the first phase of the study, we identified 16 studies that have used the FAHI. Most (82%) were conducted in North America. Only seven (44%) of the reviewed studies reported on the psychometric properties of the FAHI. In the second phase, most of the participants (37 out of 38) reported satisfaction with word clarity and content coverage whereas 34 (89%) reported satisfaction with relevance of the items, confirming the face validity of the adapted questionnaire during initial piloting. Our participants indicated that HIV impacted on their physical, functional, emotional, and social wellbeing. Their responses overlapped with items in four of the five subscales of the FAHI Questionnaire establishing its content validity. In the third phase, the internal consistency of the scale was found to be satisfactory with subscale Cronbach's α ranging from 0.55 to 0.78. The construct and convergent validity of the tool were supported by acceptable factor loadings for most of the items on the respective subscales and confirmation of expected significant correlations of the FAHI subscale scores with scores of a measure of common mental disorders. Conclusion: The adapted interviewer-administered Swahili version of FAHI questionnaire showed initial strong evidence of good psychometric properties with satisfactory internal consistency and acceptable validity (content, face, and convergent validity). It gives impetus for further validation work, especially construct validity, in similar settings before it can be used for research and clinical purposes in the entire East African region.