Ferroelectrics are widely applied in modern industrial production due to their fascinating physical properties. New findings on organic ferroelectric materials have gained the attention of researchers because they have flexible designs and are easy to produce. Here, we report on an overlooked compound, trimethylammonium bromide ((CH₃)₃NHBr), that demonstrates ferroelectricity just below room temperature. The compound undergoes a first-order paraelectric–ferroelectric phase transition at the Curie temperature (T_c) around 286 K, accompanied by significant changes in the structural, thermal and electrical properties. The space group of the compound transforms from P2₁ to P2₁/m at the Curie temperature T_c. The remnant polarization P_r is about 0.4 μC cm⁻² at 230 K and 0.25 μC cm⁻² at 243 K. This finding reveals a new pathway to design and synthesize molecular ferroelectrics.