The present research emphasizes fabrication alongside the assessment of an innovative nano-vesicular membranous system known as invasomes (NVMs) laden with Mirtazapine for rectal administration. This system could circumvent the confines of orally administered counterparts regarding dose schedules and bioavailability. Mirtazapine invasomes were tailored by amalgamating phospholipid, cineole, and ethanol through a thin-film hydration approach rooted in the Box-Behnken layout. Optimization of composition parameters used to fabricate desired NVMs' physicochemical attributes was undertaken using the Design-Expert program. The optimal MRZ-NVMs were subsequently transformed to a pH-triggered in situ rectal gel followed by animal pharmacodynamic and pharmacokinetic investigations relative to rectal plain gel and oral suspension. The optimized NVMs revealed a diameter size of 201.3 nm, a z potential of -28.8 mV, an entrapment efficiency of 81.45%, a cumulative release within 12 h of 67.29%, and a cumulative daily permeated quantity of 468.68 µg/cm. Compared to the oral suspension, pharmacokinetic studies revealed a 2.85- and 4.45-fold increase in calculated rectal bioavailability in circulation and brain, respectively. Pharmacodynamic and immunohistopathology evaluations exposed superior MRZ-NVMs attributed to the orally administered drug. Consequently, rectal MRZ-NVMs can potentially be regarded as a prospective nanoplatform with valuable pharmacokinetics and tolerability assets.