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This study examines low-temperature chemistry (LTC) enhancement by nanosecond dielectric barrier discharge (ns-DBD) plasma on a dimethyl ether (DME)/oxygen [Formula: see text] (Ar) premixture for deflagration-to-detonation transition (DDT) in a microchannel. It is found that non-equilibrium plasma generates active species and kinetically accelerates LTC of DME and DDT. In situ laser diagnostics and computational modeling examine the influence of the ns-DBDs on the LTC of DME and DDT using formaldehyde ([Formula: see text]) laser-induced fluorescence (LIF) and high-speed imaging. Firstly, high-speed imaging in combination with LIF is used to trace the presence of LTC throughout the flame front propagation and DDT. Then, competition between plasma-enhanced LTC of ignition and reduced heat release rate of combustion due to plasma-assisted partial fuel oxidation is studied with LIF. Observations of plasma-enhanced LTC effects on DDT are interpreted with the aid of detailed kinetic simulations. The results show that an appropriate number of ns-DBDs enhances LTC of DME and increases [Formula: see text] formation and low-temperature ignition, accelerating DDT. Moreover, it is found that, with many ns-DBDs, [Formula: see text] concentration decreases, indicating that excessive discharges may accelerate fuel oxidation in the premixture, reducing heat release and weakening shock–ignition coupling, inhibiting DDT.