BACKGROUND: The ideal clinic realisation and maintenance (ICRM) programme in South Africa aims to elevate primary healthcare clinic (PHC) service quality in preparation for the National Health Insurance rollout. This study investigated ICRM implementation from clinic workers' and patients' experiences in the Gauteng province. METHODS: A mixed-methods cross-sectional survey was conducted across 45 Gauteng PHCs. Anonymous semistructured interviews with 335 clinic staff explored their knowledge and experiences with the ICRM programme. Facility assessments captured structural factors impacting ICRM implementation. Log-binomial regression was used to assess factors related to confidence in ICRM implementation and improvements in ICRM certification, and thematic analysis examined patient and staff experiences. RESULTS: While 86.9% of clinical/management staff (95% CI 75.1 to 93.6) reported understanding ICRM, only 41.9% (95% CI 32.6 to 53.0) could cite specific guidelines. Enablers included guideline training (reported by 47.9% of staff, 95% CI 39.6 to 56.3) and support from district teams (44.6%, 95% CI 36.6 to 52.8). Barriers included facility size (32.9%, 95% CI 25.7 to 40.9) and infrastructure challenges (28.4%, 95% CI 21.6 to 36.2). Staff confidence in ICRM implementation was moderate (63.1%, 95% CI 56.1 to 69.6), higher when ICRM champions were present (relative risk ratio (RRR) 2.3 vs not present, 95% CI 1.0 to 5.2), guidelines were clear to staff (RRR 2.3, 95% CI 1.1 to 5.0) and sufficient training was perceived (RRR 2.7, 95% CI 1.4 to 5.3). From 2018 to 2021, 60.3% of facilities (95% CI 43.8 to 74.8) improved in ICRM classification. Compared with facilities with no status change, staff from clinics with downgraded stats were less likely to report clear guidelines (RRR 0.5, 95% CI 0.2 to 1.0) to identify an ICRM champion (RRR 0.3, 95% CI 0.1 to 0.7) or have a knowledgeable manager (RRR 0.01, 95% CI 0.01 to 0.3). CONCLUSION: Challenges in ICRM implementation persist. Staff knowledge, training and district support play significant roles, while clear guidelines, sufficient resources and effective leadership are essential for sustaining and enhancing ICRM performance.