Background: Assisted partner services (APS), or exposure notification and HIV testing for sexual partners of individuals diagnosed with HIV (index clients), have been shown to be safe and effective in clinical trials. We assessed the real-world effectiveness of APS when integrated into HIV clinics in western Kenya. Methods: In this single-arm, hybrid type 2 implementation science study, we facilitated APS implementation in 31 health facilities in Kenya by training existing health-care staff. We focused on male partner outcomes to assess the impact of APS in reaching male individuals in sub-Saharan Africa, who have lower rates of HIV testing than female individuals. Female individuals (aged ≥18 years or emancipated minor) who tested positive for HIV at participating facilities in Kenya were offered APS, consenting female participants provided contact information for all male sexual partners in the past 3 years. Male partners were notified of their potential HIV exposure and offered a choice of community-based or facility-based HIV testing services (HTS). Female index clients and male partners with HIV were followed up at 6 weeks, 6 months, and 12 months after enrolment, to assess linkage to antiretroviral treatment. Viral load was assessed at 12 months. Findings: Between May 1, 2018, and March 31, 2020, 32 722 female individuals received HTS, 1910 (6%) tested positive for HIV, of whom 1724 (90%) received APS. Female index clients named 5137 male partners (median 3 per index [IQR 2–4]), of whom 4422 (86%) were reached with exposure notification and HTS. 524 (12%) of the male partners tested were newly diagnosed with HIV and 1292 (29%) reported a previous HIV diagnosis. At 12 months follow-up, 1512 (88%) female index clients and 1621 (89%) male partners with HIV were taking ART, with few adverse events: 25 (2%) female index clients and seven (<1%) male partners reported intimate partner violence, and 60 (3%) female index clients and ten (<1%) male partners reported relationship dissolution. Interpretation: Evidence from this real-world APS scale-up project shows that APS is a safe, acceptable, and effective strategy to identify males with HIV and retain them in care. Funding: The US National Institutes of Health. © 2023 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license