It stretches 77.3 km (48.0 mi) across the western and central Greater Toronto Area from Appleby Line in Milton in the west to the Toronto-Pickering city limits in the east, where it continues east into Durham Region as Taunton Road, which itself extends 58 km (36 mi) across the length of Durham Region to its boundary with Northumberland County.

The street's name originally contained an apostrophe (before the 'S'), a suggestive of Steele's possession of the inn and land around the intersection, but it was dropped by the mid-20th century.

[6] To the west in Peel County, it was also the southern boundary of Chinguacousy Township and the Town of Brampton and the northern boundary of Toronto Township (later the Town of Mississauga between 1968 and 1974) until the municipal restructuring of 1974 brought Steeles fully within Brampton when the new city limits were set to the south at the-then future Highway 407 corridor and the Canadian National Halton Subdivision.

For instance, Toronto city councillor David Shiner invoked the 1974 agreement to veto a proposed condo development that would replace the Shops on Steeles mall.

[9] Due to an ongoing dispute on the widening and maintenance costs of Steeles, York Region's proposed Markham Bypass to Morningside Avenue has been stalled.

[10][8] The areas around the street in Toronto and York Region consists of farmland (within the Rouge National Urban Park) in the east, a mix of commercial and residential in the middle, and industrial zones near the west.

Originally, the road had a second section west of the height of the Niagara Escarpment (the location of the Crawford Lake Conservation Area), which ran from just east of Guelph Line west to the Milborough Townline on the boundary between Milton and Hamilton, but this section was renamed to Conservation Road and is thus no longer part of Steeles.

Several TTC bus routes provide service on north-south arterial roads in York Region that continue north from Toronto on a contractual basis.

On December 17, 2017, an extension of the western portion of the Line 1 subway up to Vaughan was opened, passing through York University, with a station at Steeles called Pioneer Village.

The station was named after the nearby Black Creek Pioneer Village heritage museum (as opposed to simply having a West designation as is the practice on most of the western section of the line).

Unlike TTC-contracted bus routes however, no extra fare is charged when crossing Steeles on the subway, due to the difficulty of implementing a payment-on-exit system.