A midwifery practice at the basic health facilities ensures that skilled care is available during pregnancy, labour and child birth as well as post-natal care of both mother and baby at the households. However, in Kenya there is ambiguity regarding the midwifery model in practice yet women continue to access midwifery services. The research question was about the type of midwifery practice in place and the model being followed. The broad objective of this study was to assess the effectiveness and sustainability of the functional midwifery practice model at the primary healthcare level of the health system. The specific objectives of the study were to establish the midwifery practice model, determine its effectiveness and sustainability as well as identify the challenges to the sustainability of the identified practice model at the Primary Health care settings. Research questions guiding the study were developed in tandem with the specific objectives. Literature was reviewed along the conceptual themes reflected in the specific objectives, and a theoretical model identified to ground the study as well as aid the development of a conceptual model. The study was significant in that the findings facilitate discourse on how best to ensure the challenges bedeviling the current midwifery practices are addressed, paving way for an optimally sustainable midwifery model for Kenya. This was a cross-sectional study that used both quantitative and qualitative approaches. The study sites were in Siaya sub counties of Ugenya, Ugunja, Gem and Alego-Usonga. The unit of observation and analysis was the primary health care facilities. Sampling method was both probability and non-probability sampling methods to identify the study facilities as well as the selected community respondents as appropriate. The study population included the Nurse/Midwives at the primary health care facilities, health facility administrators, the sub-county public health nurses, the community health volunteers (CHVs), and mothers within the community, who were served by the sampled health facilities. The study instruments included, individual questionnaires, observation checklists, focus group discussion guide and key informant interview guides. Quantitative data analysis was done using statistical package for social sciences (SPSS) version 24. Quantitative data was analysed using frequencies, correlation coefficient, chi square and regression analyses, while the qualitative data was analysed thematically. The findings show that the midwifery being practiced at the primary health care levels in Siaya County, is midwife-led that to a large extent, has adopted the Community Strategy and the Primary Health Care (PHC) concepts which are national concepts developed to meet the needs of the community. However, there was no guideline to that effect. The functional midwifery practiced was sustainable socially and environmentally but not financially as evidenced through the measured parameters of availability, accessibility acceptability and affordability. Data revealed that skilled birth attendance had improved, cumulatively, in the four Siaya Sub-counties (from 58% to 82%). However, daunting challenges to this sustainability were also unearthed, chief among them being insufficient and irregular funds disbursement, staffing shortage and minimal male involvement. In conclusion, the study objectives were fulfilled; the midwifery practiced in Siaya County is sustainable, being midwife-led and consistent with the team midwifery model in other developed countries, and also involving the community a lot in the promotion of skilled birth attendance. The study recommends that the model be adopted as a bottom-up team midwifery model with clear guidelines provided for standardization of the model in practice and there should be more stakeholder involvement to further enhance for its sustainability. Concerted measures should likewise be put in pace to counteract the challenges to sustainability. A home grown optical model for Kenya can be tested and fine-tuned through further research in this field.