Controlling excitons at the nanoscale in semi-conductor materials represents a formidable challenge in thequantum photonics and optoelectronics fields. Monolayers oftransition metal dichalcogenides (TMDs) offer inherent 2Dconfinement and possess significant exciton binding energies,making them promising candidates for achieving electric-field-based confinement of excitons without dissociation. Exploitingthe valley degree of freedom associated with these confinedstates further broadens the prospects for exciton engineering.Here, we show electric control of light polarization emittedfrom one-dimensional (1D) quantum-confined states in MoSe2. Building on previous reports of tunable trapping potentialsand linearly polarized emission, we extend this understanding by demonstrating how nonuniform in-plane electric fieldsenable in situ control of these effects and highlight the role of gate-tunable valley hybridization in these localized states. Theirpolarization is entirely engineered through either the 1D confinement potential’s geometry or an out-of-plane magnetic field.Controlling nonuniform in-plane electric fields in TMDs enables control of the energy (up to five times its line width),polarization state (from circular to linear), and position of 1D confined excitonic states (5 nm V-1).