Unconventional T cells, such as innate natural killer T cells (iNKT) cells, are an important part of vertebrate immune defences. iNKT recognise glycolipids through a T cell receptor (TCR) that is composed of a semi-invariant TCR α chain, paired with a restricted set of TCR β chains. Here, we show that splicing of the cognateTrav11-Traj18-Tracpre-mRNA encoding the characteristic Vα14Jα18 variable region of this semi-invariant TCR depends on the presence ofTnpo3. TheTnpo3gene encodes a nuclear transporter of the β-karyopherin family whose cargo includes various splice regulators. The block of iNKT cell development in the absence ofTnpo3can be overcome by transgenic provision of a rearrangedTrav11-Traj18-TraccDNA, indicating thatTnpo3deficiency does not interfere with the development of iNKT cells per se. Our study thus identifies a role for Tnpo3 in regulating the splicing of the pre-mRNA encoding the cognate TCRα chain of iNKT cells.