  Fermi surface is at the heart of our understanding of metals and strongly
correlated many-body systems. An abrupt change in the Fermi surface topology,
also called Lifshitz transition, can lead to the emergence of fascinating
phenomena like colossal magnetoresistance and superconductivity. While Lifshitz
transitions have been demonstrated for a broad range of materials by
equilibrium tuning of macroscopic parameters such as strain, doping, pressure
and temperature, a non-equilibrium dynamical route toward ultrafast
modification of the Fermi surface topology has not been experimentally
demonstrated. Combining time-resolved multidimensional photoemission
spectroscopy with state-of-the-art TDDFT+$U$ simulations, we introduce a novel
scheme for driving an ultrafast Lifshitz transition in the correlated type-II
Weyl semimetal T$\mathrm{_{d}}$-MoTe$_{2}$. We demonstrate that this
non-equilibrium topological electronic transition finds its microscopic origin
in the dynamical modification of the effective electronic correlations. These
results shed light on a novel ultrafast scheme for controlling the Fermi
surface topology in correlated quantum materials.
