Macrocentrus iridescens French is a polyembryonic parasitoid with a wide host and geographic range in North America. In a survey of California pistachio orchards, M. iridescens was the most common parasitoid species reared from the obliquebanded leafroller, Choristoneura rosaceana Harris. To determine its potential as a biological control agent of the obliquebanded leafroller, we conducted laboratory studies and described M. iridescens immature development. We evaluated adult female longevity, brood size, sex ratio, and host stage preference for oviposition. The parasitoid egg develops polyembryonically. At 26.8°C, larval development required 25–30 d, and pupal development 10–12 d. There was a positive relationship between mandible size and development time, although individual stages could not be determined. Adult females survived on average 15.9, 1.6, and 0.9 d at 25°C when provided with honey and fructose solution, water only, or neither, respectively. Oviposition of fertilized eggs was observed 24 h after adult eclosion, and continued for 27 d. Under laboratory conditions, each brood produced an average of 27.2 adult M. iridescens. More broods were of mixed gender (56%) than exclusively male (17%) or female (27%), with an average of 30.9, 25.8, and 20.2 adult M. iridescens per brood, respectively. M. iridescens oviposited in all host larval stages, with significantly more second (26.6%) and third (42.2%) instar larvae parasitized than first, fifth, or sixth instars. The potential of mass rearing and augmentative release of M. iridescens is discussed.