The proper timing of flowering is critical for successful reproduction. The perception of the seasonal cues of day-length changes and exposure to cold influences flowering time in many plant species through the photoperiod and vernalization pathways, respectively. Here we show that a plant homeodomain (PHD) finger-containing protein, VIN3-LIKE 1 (VIL1), participates in both the photoperiod and vernalization pathways in Arabidopsis thaliana by regulating expression of the related floral repressors FLOWERING LOCUS C (FLC) and FLOWERING LOCUS M (FLM). In the vernalization pathway, VIL1, along with VERNALIZATION INSENSITIVE 3 (VIN3), is necessary for the modifications to FLC and FLM chromatin that are associated with an epigenetically silenced state and with acquisition of competence to flower. In addition, VIL1 regulates FLM independently of VIN3 in a photoperiod-dependent manner.