The methanol-to-olefins (MTO) process has the potential to bridge future gaps in the supply of sustainable lower olefins. Promoting the selectivity of propylene and ethylene and revealing the catalytic role of active sites are challenging goals in MTO reactions. Here, we report a novel heteroatomic silicoaluminophosphate (SAPO) zeolite, SAPO-34-Ta, which incorporates active tantalum(V) sites within the framework to afford an optimal distribution of acidity. SAPO-34-Ta exhibits a remarkable total selectivity of 85.8% for propylene and ethylene with a high selectivity of 54.9% for propylene on full conversion of methanol at 400 °C. In situ and operando synchrotron powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy and inelastic neutron scattering, coupled with theoretical calculations, reveal trimethyloxonium as the key reaction intermediate, promoting the formation of first carbon-carbon bonds in olefins. The tacit cooperation between tantalum(V) and Brønsted acid sites within SAPO-34 provides an efficient platform for selective production of lower olefins from methanol.