Centimeter‐sized single crystals of Ba2LaFeNb4O15 were grown from a high‐temperature solution by using LiBO2 flux and a sealed platinum assembly. The obtained single crystals display the same physical properties as their ceramic counterparts. A frequency‐dependent dielectric permittivity maximum was found (Tm = 100 K at 5 kHz), which indicates relaxor behavior. Magnetic susceptibility measurements revealed purely paramagnetic behavior between 10 and 350 K. X‐ray diffraction measurements of Ba2LaFeNb4O15 single crystals revealed an incommensurate structure at room temperature with a bidimensional modulation characterized by vectors q1 = (α, α, 1/2) and q2 = (α, –α, 1/2) with α = 0.295(1). This crystal growth method offers a promising elaboration route to centimeter‐sized crystals of niobate‐based compounds, which may not be grown from the pure liquid phase, especially those with a tetragonal tungsten bronze (TTB) structure.