A 30 mm inner diameter iron-based superconductor (IBS) single pancake coil (SPC) was firstly fabricated and tested under a 24 T background field. This SPC was successfully made using the seven-filamentary Ba1−xKxFe2As2 (Ba122) tape by the wind-and-react method. This IBS coil shows the highest Ic value at a magnetic field reported so far. For example, the transport critical current of this Ba122 SPC achieved 35 A at 4.2 K and 10 T, which is about half of that of a short sample. This indicates that the non-insulation winding process together with the stainless steel tape is suitable for an IBS. Even more encouraging is the fact that the Ic of this SPC is still as high as 26 A under a 24 T background field, which is still about 40% of that at zero external magnetic field. These results clearly demonstrate that IBSs are very promising for high-field magnet applications.