The rise of large-scale collaborative panel studies in educational psychology and cognitive neuroscience has generated a need for fast, reliable, and valid assessments of cognitive abilities. In these studies, a detailed characterization of participants’ cognitive abilities is often unnecessary. Tests are chosen based on their ease of use and the duration and feasibility of their administration. These demands often result in the use of abbreviated measures or even related proxies, potentially compromising the reliabilities and validities of those measures. The present study evaluates the usefulness of the mini-q (Baudson & Preckel, 2016), a three-minute speeded reasoning test, as a brief assessment of general cognitive abilities in large-scale panel studies in a sample of 140 participants from diverse educational and occupational backgrounds. Participants’ test performance showed an excellent reliability and was substantially related (r = .57) to their general cognitive abilities measured with a broad test battery, supporting the test’s potential as a short screening of cognitive abilities. The largest share (54 %) of the relationship between test performance and general cognitive abilities was accounted for by participants’ working memory capacity, whereas individual differences in processing speed did not account for any part of the relationship between the two measures. Overall, our results support the notion that the mini-q can be used as a brief, reliable, and valid assessment of general cognitive abilities. However, possible disadvantages of participants with different native languages should be carefully considered due to the test’s reliance on verbal abilities.