Cumberland Peninsula, Nunavut, exposes Archean and Paleoproterozoic metamorphic rocks that are part of the Paleoproterozoic Trans-Hudson Orogen. Six metamorphic zones are present on Cumberland Peninsula. A central elongate domain, called the Touak-Sunneshine metamorphic low (TSML), contains nested muscovite+staurolite+chlorite, muscovite+andalusite, and muscovite+sillimanite zones, and parallels both regional strike and the margin of several granite-granodiorite plutons of the Qikiqtarjuaq plutonic suite. A K-feldspar+sillimanite zone constitutes much of the peninsula. Cordierite+garnet and orthopyroxene zones are spatially associated with Qikiqtarjuaq plutonic suite intrusions. To determine pressure-temperature conditions of the abundant migmatitic rocks on Cumberland Peninsula, an in-depth assessment of the application of phase diagram techniques to heterogeneous anatectic migmatitic samples was performed via thermodynamic simulations. The results pertain to migmatites in general. Key results include: the peak temperature can be recovered if just the composition of the melanosome is used to constrain the phase diagram; and temperature estimates from sample compositions comprising a combination of melanosome and leucosome can lead to over- or under-estimates of peak temperature by −25 to 50 °C. Peak metamorphic conditions on Cumberland Peninsula ranged from <4.0kbar, 545–560◦C in the muscovite+staurolite+chlorite zone to 5.6–7.6 kbar, 700–730 °C in the K-feldspar+sillimanite zone to 4.8–6.8 kbar, 730–820 °C in the cordierite+garnet and orthopyroxene zones. Microstructures indicate low-pressure metamorphism in the TSML occurred after an early deformation event and before the two dominant phases of penetrative deformation, whereas metamorphism in the K-feldspar+sillimanite zone, and locally elsewhere, was synchronous with and possibly outlasted penetrative deformation. Garnet zoning patterns and U-Pb monazite ages suggest that Cumberland Peninsula was affected by two metamorphic events. First, intrusion of the Qikiqtarjuaq plutonic suite in the northern part of the peninsula resulted in 1897 ± 8 to 1880 ± 8 Ma contact metamorphism, manifested in outwardly nested metamorphic zones. Second, 1871 ± 7 to 1853 ± 3 Ma regional metamorphism variably overprinted the entire Peninsula. Cumberland Peninsula is interpreted to have been part of the southern margin of the Rae craton, which was the upper plate in a convergent tectonic setting by ca. 1.89 Ga, before colliding with a smaller crustal block by ca. 1.87 Ga.