We systematically analyze the 6-year {\it Fermi}/LAT data of the
lobe-dominated quasars (LDQs) in the complete LDQ sample from 3CRR survey and
report the discovery of high-energy γ-ray emission from 3C 275.1. The
γ-ray emission of 3C 207 is confirmed and significant variability of the
lightcurve is identified. We do not find statistically significant γ-ray
emission from other LDQs. 3C 275.1 is the known γ-ray quasar with the
lowest core dominance parameter (i.e., R=0.11). We also show that both the
northern radio hotspot and parsec jet models can reasonably reproduce the
γ-ray data. The parsec jet model, however, is favored by the potential
γ-ray variability at the timescale of months. We suggest that some
dimmer γ-ray LDQs will be detected in the future and LDQs could
contribute non-negligibly to the extragalactic γ-ray background.Comment: 26 pages, 10 figures, 3 tables; ApJ in pres