In France, the first marine national park was set up in 2007 in the Iroise Sea, western Brittany, encompassing several Special Areas of Conservation (SAC). The park is resident to 1 of only 3 gray seal colonies in France. The at-sea habitat use of gray seals in the marine park is poorly understood and direct interactions with human activities are expected. We investigated habitat selection of gray seals within the marine park to provide spatial planning recommendations to local conservation management. We obtained data from 19 seals tracked between 2010 and 2013. We used generalized linear models to investigate their habitat selection using distance to haulout, distance to shore, bathymetry, tidal current, and sediment type as explanatory variables. The tracked individuals spent 67% of their time within the boundaries of the marine park. We investigated return trips to focus on habitat selection within the Iroise Sea. The deviance explained by the final model was 76%. Distance to haulout explained 47% of the deviance (seals selected short distances), bathymetry explained 40% (with bimodal selection for waters shallower than 50 m or deeper than 150 m), distance to shore explained 6% (selected distances less than 40 km), current explained 5% (selected weak currents), and sediment explained 2% (selected rocky areas). Habitat selection was concentrated in shallow waters located in the main archipelago of the marine park. The map of selected habitat will help identify potential conflicts of space use between seals and human activities such as fishing and leisure activities. This study has an important ecological and management value. It is the first of its kind in a marine park in France, and one of the few studies of gray seals at the periphery of their range.