U.S. Route 202 runs through the southeastern part of the U.S. state of Pennsylvania, passing through the northern and western suburbs of Philadelphia. It follows in a general southwest to northeast direction through the state, passing through West Chester, King of Prussia, Norristown, Montgomeryville, Doylestown, and New Hope.

U.S. Route 202 heads north from the Delaware border on Wilmington West Chester Pike, briefly passing through Bethel Township before entering Concord Township in Delaware County. It meets the western terminus of Pennsylvania Route 491 and heads north into Chadds Ford Township. In Painters Crossing, on the border of Chadds Ford and Concord Townships, it crosses U.S. Route 1 and U.S. Route 322, with US 322 turning north to form a concurrency with US 202. The two routes head north along the border of Chadds Ford and Thornbury Townships toward Chester County.

US 202 and US 322 cross into Chester County, heading north on Wilmington Pike along the border of Birmingham and Thornbury Townships. They intersect Pennsylvania Route 926 and head into Westtown Township. At the border of Westtown and West Goshen Townships, US 202 and US 322 head onto the limited-access West Chester Bypass, which bypasses West Chester to the east, while U.S. Route 322 Business heads north into West Chester on High Street.

The West Chester Bypass intersects Matlack Street at a traffic light, and then has interchanges with Westtown Road, Pennsylvania Route 3 (West Chester Pike), and Paoli Pike. US 322 then heads to the west on a two-lane expressway around the northern part of West Chester, and US 202 continues to the north on a four-lane expressway. It interchanges with the southern terminus of Pennsylvania Route 100, which heads to the northwest on a short expressway toward Exton. It then interchanges with Boot Road and heads into East Goshen Township briefly before entering West Whiteland Township.

On the border of West Whiteland and East Whiteland Township, US 202 interchanges with U.S. Route 30 (Lancaster Avenue). This interchange marks the eastern terminus of the U.S. Route 30 freeway in Chester County and U.S. Route 30 Business, which heads to the west on Lancaster Pike. Past this interchange, US 202 heads in a more easterly direction and interchanges with Pennsylvania Route 401 and Pennsylvania Route 29 near the Great Valley Corporate Center. It then crosses into Tredyffrin Township and heads east, intersecting Swedesford Road at a partial interchange with access only to and from the south and then Chesterbrook Boulevard. It then meets Pennsylvania Route 252, which parallels the freeway for a little distance before crossing it.

US 202 then crosses into Upper Merion Township, where it interchanges with the eastern terminus of U.S. Route 422, which heads to the northwest on a limited-access highway. It then heads toward King of Prussia, where it interchanges with Interstate 76 (the Schuylkill Expressway). I-76 provides access to the Pennsylvania Turnpike (Interstate 276), which US 202 does not have direct access to. The intersection between US 202, US 422, and I-76 is a complex interchange that was recently rebuilt. Past I-76, US 202 becomes a surface road called Dekalb Pike and passes by the King of Prussia Mall, the largest shopping mall on the East Coast of the United States and one of the largest shopping malls in the country.

It heads to the northeast and crosses over the Pennsylvania Turnpike, passing through various suburban developments. In Bridgeport, US 202 splits into two roads, with northbound US 202 heading into Bridgeport on two-lane, two-way Dekalb Street and southbound US 202 heading onto a four-lane freeway. Northbound US 202 crosses Pennsylvania Route 23 at an intersection in the center of Bridgeport and southbound US 202 features ramps that provide access to PA 23. These ramps were intended to connect to the Schuylkill Parkway, a never-built bypass of PA 23 in Upper Merion Township. Both routes cross the Schuylkill River into Norristown, with northbound US 202 heading north on one way Dekalb Street and US 202 southbound heading down two-way Markley Street. US 202 follows this one-way pair through the length of Norristown, with the route meeting back into one road at the northern border of Norristown, where southbound US 202 follows Johnson Highway between Dekalb Street and Markley Street.

US 202 then heads into East Norriton Township on the two-way Dekalb Pike. It intersects Germantown Pike and then continues into Whitpain Township. It passes over the Northeast Extension of the Pennsylvania Turnpike (Interstate 476) and intersects Pennsylvania Route 73. It then heads into Lower Gwynedd Township and then runs along the border of Lower Gwynedd and Upper Gwynedd Townships. At this point US 202 becomes a four-lane parkway and intersects Pennsylvania Route 63. It then heads into Montgomery Township and intersects Pennsylvania Route 309 (Bethlehem Pike) at an interchange. The parkway continues northeast, crossing Pennsylvania Route 463. At this intersection, the US 202 parkway narrows to two lanes.

US 202 crosses County Line Road into Warrington Township in Bucks County. Here, it comes to an intersection with Pennsylvania Route 152. The parkway continues northeast into Doylestown Township, where it comes to a cloverleaf interchange with the Pennsylvania Route 611 Doylestown Bypass. At this point, US 202 becomes a four-lane freeway running along the southern edge of Doylestown, interchanging with Main Street. The freeway then ends, and US 202 becomes a surface road called Doylestown-Buckingham Pike, intersecting Pennsylvania Route 313. It heads east into Buckingham Township, and continues to the village of Buckingham, where it crosses Pennsylvania Route 413 and then meets Pennsylvania Route 263.

It then forms a concurrency with PA 263, heading north on York Road, a part of Old York Road which connected Philadelphia to New York City. The two routes split in Lahaska, with US 202 heading east on Lower York Road. It heads into Solebury Township and heads east toward New Hope. Before reaching New Hope, it meets Pennsylvania Route 179, which heads into New Hope on the former alignment of US 202. US 202 bends to the north of New Hope and interchanges with Pennsylvania Route 32 before crossing the Delaware River into New Jersey on the New Hope-Lambertville Toll Bridge.

Before the creation of the U.S. highway system, the route had been part of Pennsylvania Route 29 between the Delaware border and West Chester and Pennsylvania Route 52 between West Chester and the New Jersey border. U.S. Route 122 was created in 1926, connecting US 22 at Whitehouse, New Jersey with Wilmington, Delaware. It became part of US 202 in 1934.

U.S. Route 202 had followed a different alignment in Chester County before the limited access alignment was built. The former alignment had US 202 exiting from what was then the West Chester By-Pass onto Paoli Pike, then later overlapping US 30 in Paoli and then turning north on what later became PA 252.

In the early 1960s, a four-lane freeway was proposed that would follow the US 202 corridor. The "Piedmont Expressway" was to be 59 miles (95 km) long, and would cost approximately $146 million. It was to serve as an outer beltway around the Philadelphia area, similar to the Capital Beltway that encircles Washington, D.C.

The Pennsylvania Department of Transportation divided the US 202 Expressway into the following eight sections:

The 202 Parkway was proposed as an 8.5-mile (13.7 km) at-grade road that would run from Montgomeryville to Doylestown north of Philadelphia, Pennsylvania. The road has been at the front of discussion and controversies around the Bucks and Montgomeryville areas for almost forty years. It was originally planned as a four-lane expressway, but in 2005 the plan was changed to a two to four lane parkway after funding for the road was cut. Construction began in November 2008 on the portion between PA 63 and PA 463, with the portion from PA 463 to the interchange with PA 611 following in January 2010. Completion of the parkway was initially expected by late 2010 with a planned opening date in early 2011. The parkway was completed by the end of 2010 between PA 63 and PA 463; this section remained closed to traffic until the remainder of the road was complete, with the exception of a small portion near PA 463. The parkway opened to traffic at 2 p.m. on December 3, 2012 at a cost of $200 million. Lieutenant Governor Jim Cawley cut the ribbon to open the parkway. The parkway has four lanes from Pennsylvania Route 63 to Pennsylvania Route 463 and two lanes from PA 463 to Pennsylvania Route 611. It has 5-foot-wide (1.5 m) shoulders, 12-foot-wide (3.7 m) walking paths on each side, sound barriers, and a 40 mph (64 km/h) speed limit. The 202 Parkway has been designated as a Pennsylvania Scenic Byway; as such, billboards are banned.

Widening of US 202 between Sumneytown Pike and PA 63 to 5 lanes (4 travel lanes plus a center left-turn lane) is also underway as an adjunct to the 202 Parkway project, linking the southern end of the Parkway with the existing 4-lane highway below Sumneytown Pike. This section is expected to be completed by late fall 2012.

Prior to the opening of the parkway, US 202 followed DeKalb Pike, PA 309, Doylestown Road, Butler Avenue, State Street, and PA 611 between Montgomery Township and Doylestown.

PennDOT has plans to widen two sections of U.S. Route 202, from U.S. Route 30 in East Whiteland Township to North Valley Road in Tredyffrin Township in Chester County, costing $175 million, and from Johnson Highway on the Norristown/East Norriton Township border to Pennsylvania Route 309 in Montgomeryville in Montgomery County, costing $130 million. Construction on both segments was expected to start in 2009. However, PennDOT has indefinitely suspended construction on both segments due to need to use money to repair structurally deficient bridges. No dates for the start of construction were slated as of December 2012.