Summary: The plastidic glutamine synthetase isoform (GS2) plays a key role in nitrogen (N) assimilation. We introduced TaGS2‐2Abpro::TaGS2‐2Ab, the favourable allele of TaGS2‐2A in the winter wheat (Triticum aestivum) variety Ji5265. Transgenic expression of TaGS2‐2Ab significantly increased GS2 abundance and GS activity in leaves. Two consecutive field experiments showed the transgenic lines had higher grain yield, spike number, grain number per spike and 1000‐grain weight than did the wild type under both low N and high N conditions. Analysis of N use‐related traits showed that transgenic expression of TaGS2‐2Ab increased root ability to acquire N, N uptake before and after flowering, remobilization of N to grains and N harvest index. Measurement of chlorophyll content and net photosynthesis rate in flag leaves during grain filling stage revealed that the transgenic lines had prolonged leaf functional duration as compared with the wild type. These results suggest that TaGS2 plays important role in N use, and the favourable allele TaGS2‐2Ab is valuable in engineering wheat with improved N use efficiency and grain yield.