In this paper, a cyan-emitting phosphor BaZrSi₃O₉:Eu²⁺ was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 380–420 nm region, and the emission intensity of the optimized BaZrSi₃O₉:Eu²⁺ was found to be 90% and 198% of that of the commercial BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu²⁺) under excitation at 405 nm and 420 nm, respectively. Upon excitation at 405 nm, the quantum efficiency of the optimized BaZrSi₃O₉:Eu²⁺ is 83% of that of BAM:Eu²⁺. The performance of this phosphor was further tested to fabricate white LED lamps. By coating BaZrSi₃O₉:Eu²⁺ with a green-emitting (Ba,Sr)₂SiO₄:Eu²⁺ and a red-emitting CaAlSiN₃:Eu²⁺ on a near-ultraviolet (405 nm) LED chip, driven by a 350 mA forward bias current, intense warm white light with a color rendering index of 90 has been produced.