Progesterone receptor (PGR), the transcription factor target for progesterone, is a pleiotropic regulator of reproductive functions and is the essential mediator of ovulation in the ovary. PGR interacts with target chromatins through the PGR response element (PRE). Recently our lab showed that PGR also exhibits unique interactions with non-canonical motifs in granulosa cells, implying the involvement of other co-regulators in PGR activities. Among the discovered motifs was RUNT, commonly recognised by the RUNX family including RUNX1. RUNX1 and PGR are known to interact with co-regulators – however the potential partnership between these transcription factors has never been shown. Here we propose RUNX1 to be a co-regulator of PGR by characterising the RUNX1 cistrome in mouse peri-ovulatory granulosa cells and demonstrating a striking interaction between PGR and RUNX1 that appears unique to granulosa cells. RUNX1 ChIP-seq identified more than 18000 RUNX1 binding sites, three-quarters of which were associated with transcriptionally active chromatin and highly enriched in in proximal promoter regions. Motif analysis indicated an enrichment of non-canonical motifs at RUNX1 binding sites, including PRE and others previously identified in PGR ChIP-seq. RUNX1 and PGR chromatin binding patterns showed a remarkably high level of correlation and that the promoter binding preference of each depends on an interaction between the two transcription factors. Proximity ligation assay in granulosa cells was used to demonstrate the presence of RUNX1 in the transcription complex involving PGR. These are the first cistromic characterisation of transcriptional control in granulosa cells and in the ovulation process and the first characterisation of PGR and RUNX1 cooperative chromatin binding. Our results suggest an interplay between PGR and RUNX1, likely through the tethering of PGR to target promoters via RUNX1. This provides a novel understanding in the molecular mechanism behind ovulation and has implications for contraceptives and specific reproductive cancer therapeutics.