Hybrid manganese halide has attracted much attention in the field of environment friendly ferroelectric and photo‐responsive multifunctional materials. Here, the highly efficient photoluminescent inorganic framework MnBr42− is utilized to conceive and synthesize a series of hybrid manganese bromide compounds RQ2MnBr4 by introducing precisely designed quasi‐spherical cations RQ+ (R = H, Me, Et, FEt, Q = quinuclidine). The accurate and effective modification of cations not only achieves the satisfactory ferroelectricity, but also enhances the photoluminescence quantum yield from 38.7% to 83.65%. Moreover, FEtQ2MnBr4 shows a highly efficient X‐ray scintillator performance, including a large range of linear response to X‐ray dose rate from 0.3 to 414.2 μGyair s−1, a high light yield of 34 438 photons per MeV, and a low detection limit of 258 nGyair s−1. This work provides an efficient strategy for the preparation of hybrid manganese halide ferroelectrics with highly efficient light‐emission and X‐ray detection. By coupling the design for high Curie temperature ferroelectrics and the modulation of photo‐responsive properties through precise modification of spherical cations, an A2MnBr4‐type hybrid ferroelectric with a high photoluminescence quantum yield of 83.65% is obtained. Moreover, the eco‐friendly crystal is promising for high performance X‐ray detectors compared with commercially available scintillators such as bismuth germanium oxide and lutetium yttrium oxyorthosilicate.