Leslie Station is located southwest of the intersection of Sheppard Avenue and Leslie Street, in North York. Primary trip generators for Leslie include North York General Hospital, located east of the station, and a collection of high-rise condominiums and big box stores to the southwest, most notably the North York IKEA (made infamous by the "IKEA Monkey" Incident of 2012). Also located one block southwest of Leslie Station is Oriole GO Station, on GO Transit's Richmond Hill Line. No direct connection is provided between the subway and GO, despite the subway station property being adjacent to the GO Train line. However, as of 2020 Richmond Hill GO Train service is provided during Monday-Friday rush hours, and only in the peak direction, so at present, this is not a major source of intermodal ridership.
As with other Line 4 stations, Leslie features wide corridors and relatively lofty ceilings. The station has 3 entrances (all accessible) and 3 fare lines, and is arranged on 3 levels that reflect the local topography as the surrounding land slopes toward the East Branch of the Don River, located east of the station. The upper level consists of a street entrance and fare line from Old Leslie Street, with a small bus terminal located inside the fare paid area. Below this is the main concourse, which is underground at its west end but at the surface at its northeast corner; this concourse includes Leslie's main entrance and fare line as a step-free walk-out to a small plaza on Sheppard Avenue.
The station's third entrance, a standalone headhouse with a fare line, can be found at the same level as the main concourse, one block east at the southwest corner of Sheppard Avenue and Leslie Street. After descending from street level, this entrance features a long pedestrian tunnel punctuated by skylights. The pedestrian tunnel is situated at track level between the eastbound and westbound tracks, and connects directly to the east end of the station platform.
Below the main concourse is the platform level. As with most other stations on Line 4, Leslie features an island platform currently sized to hold a 4-car train, but with knockout panels allowing future expansion to 6-car trains. Leslie has 2 knockout panels at the east end of the platform, on either side of where the pedestrian tunnel from the east entrance joins the platform.