American martens (Martes americana) in the northern Lower Peninsula of Michigan (NLP) represent a re-introduced and isolated population that is the southern-most distributed marten population in eastern North America. During 2005–2006 we conducted a radiotelemetry and track-survey study of martens in the NLP. We estimated home-range size and patterns of habitat use in order to develop a spatial model to predict distribution of marten habitat. Marten home ranges were comprised of more (>75%) upland deciduous and upland mixed forest compared to the landscape, which included ≤60% of these cover types. Within core areas, martens selected upland conifer stands. Our Penrose habitat model identified <25% of the NLP as primary marten habitat. Further, 70% of marten habitat patches were <1000 ha in size and were isolated by an average of 5.3 km (SE = 2.0). Our marten habitat model identifies focal areas for surveying and monitoring populations and sites for supplementation or re-introduction. Our model also highlights the need for managers to better coordinate active landscape-scale management of wildlife and forests to reduce fragmentation impacts on extant and reintroduced marten populations.