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Constraining the onset of dynamic recrystallization (DRX) and its effects on the mechanical properties of firn is crucial for firn densification modeling. To that end, samples from a depth of 13 m in a Summit, Greenland (72°35′N, 38°25′W) firn core were subjected to creep tests at −14°C and 0.21 MPa compressive stress to strains of 7%, 12%, 18%, and 29%. Microstructural analyses using thin‐section imaging and microcomputed x‐ray tomography (micro‐CT) revealed smaller grain sizes, reduced specific surface area and connectivity, and increased density in relation to reduced porosity as the strain increases. These results show that DRX occurs in firn under creep, with strain‐induced boundary migration (SIBM) and nucleation and growth starting at ∼7%. DRX leads to elongated grains, reduced grain size, and the development of a preferred crystallographic orientation, indicating that DRX occurs by both SIBM and nucleation and growth. Plain Language Summary: Firn is multi‐year snow that undergoes densification due to the load from the snow overburden and from sintering. Understanding firn densification is important for interpreting ice core records, predicting ice sheet mass balance and elevation changes, and studying climate change effects. Previous densification models focused on accumulation rate and temperature, overlooking the role of recrystallization. To address this gap, compression tests were performed on Greenland firn samples from a depth of 13 m. The deformation resulted in reduced median grain size, preferred crystallographic orientation, and increased density. Our findings indicate that dynamic recrystallization starts when the firn is subjected to a strain of about 7% through boundary migration of old grains, around which new stress‐free grains also start to form. Key Points: Dynamic Recrystallization occurs in firn through strain‐induced boundary migration, and nucleation and growthAverage grain size in firn decreases under constant temperature and compressive stress in firn [ABSTRACT FROM AUTHOR]