The Impulsive Behavior Short Scale-8 (I-8) measures the psychological construct of impulsivity with four subscales comprising two items each (completion time < 1 min). The aim of the present study was threefold: (1) to assess the psychometric properties (objectivity, reliability, and validity) of the English-language I-8; (2) to compare these psychometric properties with those of the original German-language source version of the scale; and (3) to test the cross-national comparability of the scale via measurement invariance tests. For this purpose, we used heterogeneous quota samples from the UK and Germany. Our results indicate that I-8 is a reliable and valid short scale with highly comparable psychometric properties across both language versions. In addition, I-8 showed a highly similar correlational pattern with various extraneous variables across the two nations. Furthermore, partial scalar invariance and full invariance of residual variances held, allowing the comparison of latent means and observed (co)variances across nations. I-8 lends itself as a measure of impulsive behavior especially in surveys in which assessment time is limited, such as in large-scale cross-national surveys.