Electronic spins of nitrogen–vacancy centres in diamond constitute a promising system for micro- and nanoscale magnetic sensing1, 2, 3–4, because of their operation under ambient conditions5, ease of placement in close proximity to sensing targets6 and biological compatibility7. At high densities, the electronic spins interact through dipolar coupling, which typically limits8 but can also potentially enhance9 sensing performance. Here we report the experimental demonstration of many-body signal amplification in a solid-state, room-temperature quantum sensor. Our approach uses time-reversed two-axis-twisting interactions, engineered through dynamical control of the quantization axis and Floquet engineering10 in a two-dimensional ensemble of nitrogen–vacancy centres. We observe that optimal amplification occurs when the backward evolution time equals twice the forward evolution time, in sharp contrast to the conventional Loschmidt echo11,12. These observations can be understood as resulting from an underlying time-reversed mirror symmetry of the microscopic dynamics, providing key insights into signal amplification and opportunities for practical entanglement-enhanced quantum sensing. The experimental demonstration of many-body signal amplification in a solid-state, room-temperature quantum sensor is reported.