Kīlauea Volcano is underlain by a complex, laterally-extensive magmatic plumbing system. Although in recent decades it has mainly erupted through vents along the middle East Rift Zone and summit caldera, eruptions can occur anywhere along its two laterally extensive rift zones, as demonstrated by the dramatic eruptive activity of 2018. Forecasting eruptive activity requires an understanding of whether an episode of volcano-seismic unrest at Kīlauea or a similar volcano is caused directly at the edges of an active magmatic intrusion or reservoir, or in a volume of wall rock at a distance from the intrusion. Seismic unrest in Kīlauea’s Upper East Rift Zone (UERZ) has to date been interpreted as the result of either magma intrusion in this region of the volcano or of stresses due to seaward flank migration. However, recent observations suggest that UERZ seismicity may result from variable pressurization of Kīlauea’s summit magma system. We analyze seismic and deformation (multi-temporal InSAR and GPS) data during a period of variable summit deformation and UERZ seismicity in mid- to late-2007 and calculate Coulomb stress changes on UERZ faults due to modeled summit inflation or deflation. UERZ seismicity during our study period can be explained entirely by stresses arising from pressure changes within Kīlauea’s two summit reservoirs. Furthermore, a comparison of UERZ fault plane solutions (FPS) calculated for this study to published UERZ FPS for previous periods suggests the UERZ has undergone a transition from a mechanically-strong, discontinuous and immature magma transport system to a mature, mechanically-weak and fully-connected transport system over the course of the 1983-2018 eruption.