The olive-sided flycatcher (Contopus cooperi) has experienced an important decline throughout its distribution range. The implementation of conservation measures to promote the recovery of this migratory species is, however, limited by a lack of knowledge concerning its nesting ecology. The objectives of this study were to obtain information regarding the habitat used by the olive-sided flycatcher in managed boreal forests of eastern North America, and its nesting success. During 2015 and 2016, a total of 38 sites with at least 1 olive-sided flycatcher were located, and 13 nests were found—all situated in live black spruce (Picea mariana). The nesting success was estimated at 53.8 %, and predation, most likely by the gray jay (Perisoreus canadensis), and adverse weather conditions were considered to be the most likely causes of nest failure. At the landscape level, the olive-sided flycatcher selected mixed forest stands, forest edges and recent clear-cuts. This study provides important information on the nesting ecology of this species in the eastern part of its distribution range.