Multi-drug resistance (MDR) poses a significant challenge to cancer treatment. Targeting ATP-binding cassette subfamily B member 1 (ABCB1) is a viable strategy for overcoming MDR. This study examined the preclinical in vitro and animal studies that used gilteritinib, a FLT3 inhibitor that reverses ABCB1-mediated MDR. At nontoxic levels, gilteritinib significantly increased the susceptibility of cancer cells overexpressing ABCB1 to chemotherapeutic drugs. Furthermore, it impaired the development of drug-resistant cell colonies and 3D spheroids. Studies on the reversal mechanism have shown that gilteritinib can directly bind to the drug-binding site of ABCB1, inhibiting drug efflux activity. Consequently, the substrate’s drug cytotoxicity increases in MDR cells. Furthermore, gilteritinib increased ATPase activity while leaving ABCB1 expression and subcellular distribution unchanged and inhibited AKT or ERK activation. Docking analysis indicated that Gilteritinib could interact with the drug-binding site of the ABCB1 transporter. In vivo studies have shown that gilteritinib improves the antitumor efficacy of paclitaxel in nude mice without obvious toxic effects. In conclusion, our preclinical investigations show that gilteritinib has the potential to successfully overcome ABCB1-mediated MDR in a clinical environment when combined with substrate medicines.