A new red phosphor based on the Li1+x (Ta1−zNbz)1−xTixO3 (LTNT, 0.05 ≤ x ≤ 0.25, 0 ≤ z ≤ 0.625) solid solution as a host material has been synthesized. This host material is known as an M-phase and has a superstructure similar to that of the Li1+x−yNb1−x−3yTix+4yO3 (LNT) solid solution. An Eu3+-doped LTNT has been prepared by sintering at 1413 K–1433 K for 24 h in a conventional electric furnace; the optimal sintering temperature for obtaining higher photoluminescence (PL) intensity was found to be 1423 K. Interestingly, bright red emission due to the hypersensitive 5D0-7F2 transition in Eu3+ was observed under direct excitation of the 4f electron at 541 (7F0-5D1) or 398 nm (7F0-5L6). The PL intensity of the LTNT phosphor was found to be dependent on the concentration of Eu3+, Ti4+, Nb5+, and Ta5+ ions. The PL intensity upon excitation at 541 nm was higher than that at 398 nm with decreasing Nb2O5 content in the LTNT host material. The highest PL intensity was achieved for the composition Li1.11Ta0.89Ti0.11O3 doped with 2.5 wt% of Eu2O3.