<p>Among the various cations, the Fe³⁺ ion is one of the most critical transition metal ions in living cells for many cellular functions and enzymatic activities. The decrease or overloading of Fe³⁺ can lead to different disruptions in humans. Also, Fe³⁺, highly toxic, is very common in all industrial wastewater. So, the design and synthesis of Fe³⁺ chelators as high-selective chemosensors are essential for detecting Fe³⁺. In this paper, 6-(6-bromopyridin-2-yl)benzo[4,5]imidazo[1,2-<i>c</i>]quinazoline (BQ) as a novel colorimetric sensor for sensing of Fe³⁺ was synthesized and characterized by ¹H-NMR, ¹³C-NMR, IR, and mass spectrometry. The sensing behavior of BQ toward various cations has been analyzed via colorimetric detection and UV–vis spectroscopy. The BQ was observed to have excellent selectivity and sensitivity to the presence of Fe³⁺ among the tested ions in aqueous media. Interestingly, the BQ can selectively recognize Fe³⁺ ions with the naked eye via the color change of colorless to yellow. The effect of pH on the stability and absorption of BQ towards Fe³⁺ was studied. The results of pH studies showed that the absorbance of complex BQ/Fe³⁺ remains stable between pH 5–10. Moreover, to determine the sensing behavior of BQ to Fe³⁺, the mole ratio method was carried out. The binding stoichiometry of BQ/Fe³⁺ was assessed by using Job’s plot and indicated the 1:1 binding ratio between BQ and Fe³⁺. Under the optimal conditions, there was a good linear relationship (correlation coefficient R² = 0.9886) in Fe³⁺ concentration in the 58–114 μM range, with a detection limit of 53.39 nM.</p>