Mn2+‐activated halide double perovskites (HDPs) are found to show promising luminescent behavior and have great potential for optoelectronic applications. However, such interesting materials hitherto are only limited to compounds with a monotonous three‐dimensional structure and show a low photoluminescence quantum yield (PLQY). Herein, an Mn2+‐doped two‐dimensional (2D) layered HDP PPA4NaInCl8 (PPA+ = C6H5(CH2)3NH3+) showing promising photoluminescence properties is reported. The large separation between the adjacent inorganic sheets and the good dissolution of Mn2+ in the layered structure endow PPA4NaInCl8:Mn2+ with efficient red emission and a record PLQY of 69.90%. The spectroscopic analyses and density functional theory calculations indicate that the inherent absorption and luminescence stem from the inserted organic cations PPA+ in PPA4NaInCl8. An energy transfer process occurs between the singlet excitons from PPA+ and Mn2+, resulting in tunable emission accompanied by the variation of Mn2+ concentration. These results provide several new fundamental insights on doping and doped 2D layered HDPs, which enhances the understanding of structure−property relations in this important family.