Inhibition of the metabolic regulator AMP-activated protein kinase (AMPK) is increasingly being investigated for its therapeutic potential in diseases where AMPK hyperactivity results in poor prognoses, as in established cancers and neurodegeneration. However, AMPK-inhibitory tool compounds are largely limited to compound C, which has a poor selectivity profile. Here we identify the pyrimidine derivative SBI-0206965 as a direct AMPK inhibitor. SBI-0206965 inhibits AMPK with 40-fold greater potency, and markedly lower kinase promiscuity, than compound C, and inhibits cellular AMPK signalling. Biochemical characterization reveals SBI-0206965 is a mixed type inhibitor. A co-crystal structure of the AMPK kinase domain/SBI-0206965 complex shows the drug occupies a pocket that partially overlaps the ATP active site in a type IIb inhibitor manner. SBI-0206965 has utility as a tool compound for investigating physiological roles for AMPK, and provides fresh impetus to small-molecule AMPK inhibitor therapeutic development.