We demonstrate continuous tuning of a terahertz quantum cascade wire laser over a broad range of ∼330 GHz (∼8.6% of the 3.85 THz center frequency) with single-mode operation. Tuning is achieved with a narrow laser ridge (∼λ(o)/8) and a moveable MEMS (microelectromechanical systems) side object (plunger) to manipulate the transverse optical mode. The frictionless MEMS plunger enables continuous and reversible tuning. We demonstrate ∼30 GHz redshift tuning using a silicon plunger and ∼300 GHz blueshift tuning using a metal plunger. The blueshift tuning range is limited by the bandwidth of the gain medium rather than the tuning mechanism.