Glass　fibre　reinforced　polymer　(GFRP)　composite　bars　can　be　used　as　internal　reinforcement　for　concrete　structures　built　in　harsh　environmental　and　service　conditions.　Their　utilisation　as　longitudinal　reinforcement　for　compression　members　is　not　widely　recommended　though　due　to　the　anisotropic　nature　of　FRP,　their　complex　failure　modes,　and　limited　research,　especially　for　slender　bars.　A　more　recent　innovation　has　resulted　in　the　wrapping　(confinement)　of　GFRP　bars　with　FRP　composites　oriented　in　the　hoop　direction.　These　confined　bars　have　demonstrated　promising　improvement　in　FRP　bar　compressive　behaviour　and　ductility.　In　the　current　study,　the　experimental　compressive　behaviour　of　eighty　short　and　slender　FRP-confined　GFRP　bars　is　reported　and　a　compressive　strength　model　is　proposed.　The　experimental　parameters　investigated　are　(i)　wrapping　layers　(i.e.　one,　two,　and　three　layers　oriented　±　83.3°　to　the　longitudinal　axis　of　the　bar),　and　(ii)　slenderness　ratios　(i.e.　15,　30,　45,　and　60).　The　resulting　compressive　load　capacity　and　strength,　stress–strain　behaviour,　and　failure　modes　are　then　reported　for　each　tested　bar.　Test　results　indicate　that　an　increase　in　slenderness　results　in　decreased　strength.　In　addition,　failure　modes　shifted　from　splitting　to　buckling　of　the　longitudinal　fibres.　GFRP　bars　with　at　least　two　winding　layers　had　a　significantly　higher　compressive　strength　than　the　control　GFRP　bar　(not　including　winding)　and　they　also　exhibited　bi-linear　stress–strain　behaviour　as　well　as　ductile　failure　modes.　A　compressive　strength　prediction　model　is　then　developed,　which　is　based　on　the　modification　of　the　Johnson-Euler　buckling　theory　and　correlates　well　with　the　experimental　results.　The　research　presented　herein　has　the　potential　to　contribute　to　the　development　of　design　guidelines　for　concrete　compression　members,　such　as　columns,　piers　and　piles,　that　are　reinforced　with　FRP-confined　GFRP　bars.　©　2023　Elsevier　Ltd