The convent bears the imprint of Portscheller. Originally surrounded by a five-foot wall enclosure, it is sited perpendicular to the street facing the church to the east. Its long rectangular plan is distinctive for its angled side elevations with pedimented Doric pilasters, while its exterior is profiled by a steeply pitched shingle roof topped by a central hipped-roof cupola, an unusual Victorian period architectural feature for Roma.
Behind the convent, at 708 Estrella, the Old Mission Church is composed of two gable-end, rectangular, sandstone buildings forming an ell. According to local tradition, the smaller of the two, along Lincoln Avenue, served as a chapel prior to 1848 when priests visited Rancho de Buena Vista from Mier.