St Moritz sits at 1,856 metres elevation in the Upper Engadin valley, a broad glaciated basin in southeast Switzerland's canton of Graubünden. The valley stretches approximately 80 kilometres from Maloja Pass to the Austrian border, with St Moritz positioned centrally amongst a chain of lakes including Lake St Moritz, Lake Silvaplana and Lake Sils. Piz Bernina at 4,049 metres dominates the southern skyline 15 kilometres away as the Eastern Alps' highest summit, whilst the Albula range rises north of the valley. The Corviglia ski area occupies the southern slopes of Piz Nair directly above the resort, with south-facing exposure delivering sun from early morning through afternoon.

The town divides into St Moritz Dorf on the hillside and St Moritz Bad in the valley floor, with neighbouring Celerina 2 kilometres northeast and Samedan 4 kilometres distant serving as the Upper Engadin's administrative capital. The area lies within the Maloja administrative region, historically a Romansh-speaking territory now predominantly German and Italian-speaking due to tourism growth. Engadin Airport in Samedan sits 5 kilometres from St Moritz at 1,707 metres elevation, Europe's second-highest commercial airfield, handling private jets and charters but no scheduled passenger service. The frozen lake hosts winter events including polo and horse racing on its 1,800-metre-elevation surface.

Road access centres on the Julier Pass from the north, open year-round and reaching 2,284 metres elevation via a well-maintained route from Chur and Thusis. The A13 motorway from Zurich runs to Thusis, where Route 3 continues via Tiefencastel and Savognin to Silvaplana, with the final segment on Route 27 into St Moritz. The Maloja Pass at 1,815 metres connects southwest to Italy via Val Bregaglia and Chiavenna, descending steeply through 22 hairpins toward Lake Como. Zurich lies approximately 200 kilometres northwest with a 3-hour drive, whilst Milan sits 180 kilometres south requiring 3 hours via Italian motorways and the Maloja or Bernina approaches.

Zurich Airport (ZRH) serves as the primary international gateway 220 kilometres distant, with Milan Malpensa (MXP) 180 kilometres and Milan Bergamo (BGY) 155 kilometres offering southern alternatives. The Rhaetian Railway operates direct trains from Zurich Hauptbahnhof to St Moritz in 3 hours via the UNESCO-listed Albula line through Chur, Filisur and the Albula Tunnel. Trains also connect south via the Bernina Pass to Tirano in Italy, whilst the Vereina Tunnel links the Lower Engadin to Klosters. PostBus services cover valley villages and connect Maloja Pass routes to Lugano and routes east through the Swiss National Park to South Tyrol.