Detrital zircons from quartzites constrain the timing of deposition, provenance, and basin evolution of the Grenville supergroup in the Adirondack Lowlands. Three samples from the stratigraphic succession yield maximum depositional ages of 1284 ± 16 Ma to 1257.6 ± 16 Ma. Shifts in provenance from rifting (unimodal volcanic), carbonate platform (Laurentian interior), deep-water clastics (southern Adirondack arc), to final basin fill (Laurentian interior) are documented. The Trans-Adirondack backarc basin is one of several that opened at ca. 1.30 Ga, filled with thick carbonate-dominated sequences, and closed during the Elzevirian orogeny (ca. 1245–1220 Ma), terminating widespread extension across the leading edge of southeast Laurentia.