The service normally begins from Linden in Wilmette and ends at Howard on Chicago's north border, passing through the city of Evanston.

During weekday rush hours, the Purple Line extends another 10.3 miles (16.6 km) south on the North Side Main Line from Howard to downtown Chicago running express from Howard to Belmont, with a single stop at Wilson, and then making all local stops from Belmont to the Loop.

The tracks are split on grade separated structures to allow Yellow Line trains to enter the junction from the west.

After the North Shore Line ceased operations in 1963, the outer tracks in this area were rarely used and received next to no maintenance; they were permanently taken out of service in 1976.

[8] As a result of the Brown Line construction and in effort to minimize delays, trains now stop one station north at Sheridan Road before evening Cubs games.

The Purple Line Express operates rush hour service between Linden and the Loop on weekday morning only from 5:15 a.m. to 9:20 a.m. (northbound) and from 5:55 a.m. to 10:05 a.m.

The new terminal was established without permission of Wilmette residents, who feared rail service would encourage construction of large apartment buildings in the affluent community.

[15] In 1922, the surface level section of the North Side 'L' was elevated onto a concrete embankment structure between Leland Avenue and Howard Street and was expanded from two to four tracks, allowing complete express service from Wilmette and Evanston to downtown Chicago.

[19] Right-of-way and trackage used by the Evanston Branch and the North–South Route (today's Red Line) between Leland Avenue and the Wilmette terminal was purchased by the CTA in 1953 from the Chicago, Milwaukee, St. Paul and Pacific Railroad.

Prior to this, Evanston shuttle trains had to be equipped with trolley poles and power collected through overhead catenary wires (similar to the Yellow Line before its conversion to third rail in 2004).

Since parts of the line are at grade level, some community members initially resisted the conversion and worried the proximity of the rail would be hazardous.

[23] By the end of 1976, the Evanston Express ran nonstop between Howard and Merchandise Mart, no longer stopping at Morse, Loyola, Wilson or Chicago/Franklin.

[24] However, on January 20, 1989, express trains once more began making additional stops outside the Loop, at the Belmont and Fullerton stations, in order to relieve overcrowding on the rapidly growing Ravenswood branch (now the Brown Line).

The poor condition of the century-old viaducts forced the implementation of permanent slow zones and were a point of contention for many Evanston politicians.

[30] The Main Street viaduct was completely replaced over the weekend of November 12–13, 2005, requiring the temporary shutdown of the Purple Line.

[33] The Purple Line's Howard terminal underwent a major renovation from 2006 until 2009, during that time it was completely rebuilt and made ADA-accessible.

[37] The CTA budget crisis continued into 2007 and the Purple Line Express was once again selected as one of several routes to be eliminated if additional funding was not provided.

[38] However, the final plan retained the downtown service, making the stop at the Sheridan station permanent to supplement the Red Line and provide additional capacity on the system following the elimination of thirty-nine bus routes.

[39] The service cuts were scheduled to be implemented on September 16, 2007,[40] but the CTA received a last-minute $24 million advance on its 2008 operating subsidy, postponing the changes until November 4, 2007.

[41] A last-minute $21 million grant from the governor once again postponed the changes to January 20, 2008,[42] this time including the elimination of 42 additional routes.

Beginning April 2, 2007, operation on the Purple, Brown and Red Lines between Addison and Armitage was restricted to three tracks, down from the previous four, due to construction at the Fullerton and Belmont stations.

However, this is a study and the final form of the Circle Line and its effects on current CTA rail service, The project was canceled.