The airline was established in February 1985 as Express Airlines I with the intent of offering regional airline passenger feed to a code sharing, major airline’s hub. Express I began its first code sharing agreement with Republic Airlines in May 1985. Republic was the dominant carrier in Memphis but, in keeping with the hub-and-spoke concept, wanted to add more smaller cities and free up its larger DC-9 jets to serve longer stage-length routes. Express I was able to accomplish this by beginning service on June 1, 1985, to 3 cities using BAe Jetstream 31 aircraft. Within six months, Express Airlines I was operating in ten markets using nine Jetstream 31s and two Saab 340 aircraft.
On December 15, 1985, a second contract opened operations at a Republic Airlines home base at Minneapolis-St. Paul. By its first anniversary, Republic Express was operating 20 Jetstream 31s and seven Saab 340s in 32 markets. In Spring 1986, Northwest Airlines announced the acquisition of Republic, which was completed on October 1, 1986, following regulatory and shareholder approvals.
Over the next decade, Express I provided airline services to 56 cities in the Southeast and upper Mid-West. In 1997, Northwest Airlines elected to make changes in the structure of Express I, which was a privately held company. On April 1, 1997, Express I became a wholly owned subsidiary of Northwest Airlines. In order to consolidate the many Airlink systems operated at that time, Express I transferred flying at Minneapolis-St. Paul, allowing it to concentrate on the Memphis Hub.
In August 1997, Express I moved its corporate headquarters to Memphis, allowing all the various departments to function from its main base of operations. On 7 May 1999, Express I announced a major transition into the jet age as its parent company announced that Express would be the launch operator of the Bombardier Canadair Regional Jet (CRJ) at Northwest. This award was for a minimum of 42 CRJs designated to operate as Northwest Jet Airlink. Delivery of the CRJs began in April 2000 and the first Northwest CRJ lifted into the sky on June 1, 2000, bound for Greenville-Spartanburg International Airport (GSP). The first CRJ (N8390A) was named "The Spirit of Memphis Belle," although it has since been repainted into Delta Connection colors, but the title "The Spirit of Memphis Belle" still remains painted on the forward part of the fuselage. Express I changed its name to Pinnacle Airlines on May 8, 2002.