The Eagles, along with the Pittsburgh Steelers and the now-defunct Cincinnati Reds, joined the NFL as expansion teams. Wray became the Eagles' first head coach after being convinced by Bell, his former teammate at Penn, to take the position. The team originally planned to play their home games at Shibe Park, which was the home of the Philadelphia Athletics baseball club. When negotiations fell through the team managed to make a deal with the Athletics' crosstown rival, the Philadelphia Phillies, to play at the Baker Bowl.

The Eagles played their first game on October 15, 1933, against the New York Giants at the Polo Grounds in New York City; they lost, 56—0. The Eagles struggled over the course of their first decade, never winning more than four games. Their best finish was in their second season, 1934, when they tied for third in the East. For the most part, the Eagles' early rosters consisted of former Penn, Temple, and Villanova players who played for a few years before going on to other things.

From 1936 to 1939, the Eagles played at Municipal Stadium in South Philadelphia. In 1940, Bell balked at a 66% rent increase plus 10% of the gate receipts proposed by the city for using the stadium and signed a lease for Shibe Park (renamed Connie Mack Stadium in 1954). The Eagles would also be able to play night games as Shibe Park had installed lights the year before. In the 1941 season, the Eagles played their home opener at Municipal Stadium, but then moved to Shibe Park. To accommodate football at Shibe Park during the winter, management set up stands in right field, parallel to 20th Street. Some 20 feet high, these "east stands" had 22 rows of seats. The goalposts stood along the first base line and in left field. The uncovered east stands enlarged the park's capacity to over 39,000, but the Eagles rarely drew more than 25,000 to 30,000. The team finished the 1937 season 2—8—1 and would continue to struggle over the next three seasons.

After assuming ownership, Thompson promptly hired Earle "Greasy" Neale as the team's head coach. During the first years under Neale, the team continued to struggle by finishing the 1941 season with a 2—8—1 record. The 1942 season showed no improvement as the team went 2—9.

Undeterred, the young squad rebounded in 1948 to return to the NFL Championship game. With home-field advantage (and a blinding snowstorm) on their side, the Eagles won their first NFL Championship against the Chicago Cardinals, by a score of 7—0. The only score came in the fourth quarter when Steve Van Buren ran for a 5-yard touchdown. Because of the severe weather, few fans witnessed the joyous occasion.

Pete Pihos, Eagles tight end from 1947 to 1955, was inducted into Pro Football's Hall of Fame in 1970.

Before the start of the 1949 season, the team was sold by Thompson to a syndicate of 100 buyers, known as the "Happy Hundred", each of whom paid $3,000 for a share of the team. While the leader of the "Happy Hundred" was noted Philadelphia businessman James P. Clark, one unsung investor was Leonard Tose, a name that would eventually become very familiar to Eagles fans.

The team returned to the NFL Championship game for the third consecutive year. The Eagles were favored by a touchdown, and won 14—0 for their second consecutive title-game shutout. Running back Steve Van Buren rushed for 196 yards on 31 carries for the Eagles, and their defense held the Rams to just 21 yards on the ground. Chuck Bednarik was selected as the first overall pick in the 1949 NFL Draft. An All-American lineman/linebacker from the University of Pennsylvania, Bednarik would go on to become one of the greatest and most beloved players in Eagles history.

With the new decade came another turn in team fortunes. In 1950, the Eagles were slated to open the season against AAFC champion Cleveland Browns, who had just (along with the other AAFC franchises) joined the NFL. The Eagles were expected to make short work of the Browns, who at the time were widely considered the dominant team in a lesser league. However, the Browns lit up the Eagles' vaunted defense for 487 total yards, including 246 passing yards, in a 35—10 rout. The Eagles never really recovered, and finished 6—6.

Khayat lost his first two games but won six of the season's last nine, thanks largely to the efforts of the defense, led by All-Pro safety Bill Bradley, who led the NFL in interceptions (11) and interception return yardage (248).

The team regressed in 1972 to finish 2—11—1, and Khayat was released. The two wins (both on the road) proved to be surprises, however. Philadelphia beat the Kansas City Chiefs (which had had the best record in the AFC a year before) 21—20 and the Houston Oilers 18—17 on six field goals by kicker Tom Dempsey. The latter game had been called the "Johnny Rodgers Bowl," because the loser, in finishing last in the league, would gain the first overall pick in the 1973 NFL Draft, which was then presumed to be Nebraska wingback Johnny Rodgers, the Heisman Trophy winner. With their loss, the Oilers got first pick and took University of Tampa defensive end John Matuszak (who later faced Philadelphia in Super Bowl XV). With the second overall pick, the Eagles went with USC tight end Charle Young.

Khayat was replaced by offensive guru Mike McCormack, for the 1973 season. Aided by the skills of Roman Gabriel and towering young receiver Harold Carmichael, they managed to infuse a bit of vitality into a previously moribund offense.

New general manager Jim Murray also began to add talent on the defensive side of the line, most notably through the addition of future Pro Bowl linebacker Bill Bergey in 1974. Overall, however, the team was still mired in mediocrity. McCormack was fired after a 4—10 1975 season.

In 1935, Bell proposed an annual college draft to equalize talent across the league. The draft was a revolutionary concept in professional sports. Having teams select players in inverse order of their finish in the standings, a practice still followed today, strove to increase fan interest by guaranteeing that even the worst teams would have the opportunity for annual infusions of the best college talent. Between 1927 (when the NFL changed from a sprawling Midwestern-based association to a narrower, major-market league) and 1934, a triopoly of three teams (the Chicago Bears, New York Giants, and Green Bay Packers) had won all but one title (the exception being the Providence Steam Roller of 1928). By 1936 the club had suffered significant financial losses and was sold through a public auction. Bert Bell was the only bidder and became the sole owner of the team. Wray refused a reduction in his salary and left the team. Bell assumed the head coaching position and led the team to a record of 1—11, for last place in the league.

The Eagles played their first game on October 15, 1933, against the New York Giants at the Polo Grounds in New York City; they lost, 56—0. The Eagles struggled over the course of their first decade, never winning more than four games. Their best finish was in their second season, 1934, when they tied for third in the East. For the most part, the Eagles' early rosters consisted of former Penn, Temple, and Villanova players who played for a few years before going on to other things.

In 1943, when manpower shortages stemming from World War II made it impossible to fill the roster, the team merged with the Steelers forming the "Phil-Pitt Eagles", known as the Steagles. Greasy Neale coached the team along with Steelers head coach Walt Kiesling. The team finished the season with a 5—4—1 record. The merger, never intended as a permanent arrangement, was dissolved at the end of the season.

In 1944, led by head coach Greasy Neale and running back Steve Van Buren, the Eagles had their first winning season in team history. After two more second-place finishes in 1945 and 1946, the team reached the NFL Championship game for the first time in 1947. Van Buren, Pete Pihos, and Bosh Pritchard fought valiantly, but the young team fell to the Chicago Cardinals, 28—21 at Chicago's Comiskey Park.

Steve Van Buren, Eagles halfback from 1944 to 1951, was inducted into Pro Football's Hall of Fame in 1965.

Chuck Bednarik, Eagles linebacker and center from 1949 to 1962, was inducted into Pro Football's Hall of Fame in 1967.

Greasy Neale retired after the 1950 season and was replaced by Bo McMillin. Two games into the 1951 season, McMillin was forced to retire due to terminal stomach cancer. Wayne Millner finished out the season before being replaced by Jim Trimble.

While the remnants of the great 1940s teams managed to stay competitive for the first few years of the decade, and while younger players like Bobby Walston and Sonny Jurgensen occasionally provided infusions of talent, the team lacked the stuff of true greatness for most of the 1950s.

After the 1957 season, the Eagles moved from Connie Mack Stadium to Franklin Field at the University of Pennsylvania. Franklin Field would seat over 60,000 for the Eagles, whereas Connie Mack had a capacity of 39,000. The field's grass was replaced by AstroTurf in 1969, making it the first NFL stadium to use artificial turf.

In 1969, Leonard Tose bought the team from Wolman for $16.155 million (equal to $119,374,015 today), a new record for a professional sports franchise. Tose's first official act was to fire Coach Joe Kuharich after a disappointing 24—41—1 record during his five-year reign. He followed this by naming former Eagles receiving great Pete Retzlaff as General Manager and Jerry Williams as coach.

With the merger of the NFL and AFL in 1970, the Eagles were placed in the NFC East Division with the New York Giants, Washington Redskins, and Dallas Cowboys. The Eagles' heated rivalry with the Giants is the oldest of the NFC East rivalries, dating back to 1933, and is often cited as one of the best rivalries in the NFL. 1970 was also the last season for the Eagles at Franklin Field; the team finished the first post-merger season in last place in their division at 3—10—1.

In 1971, the Eagles moved to the new Veterans Stadium. In its first season, the “Vet” was widely acclaimed as a triumph of ultra-modern sports engineering, a consensus that was short-lived, as was Williams' tenure as head coach. After a 3—10—1 record in 1970 and three consecutive blowout losses to Cincinnati, Dallas, and San Francisco to open the 1971 season, Williams was fired and replaced by assistant coach Ed Khayat, a defensive lineman on the Eagles' 1960 NFL championship team. Williams and Khayat were hampered by Retzlaff's decision to trade longtime starting quarterback Norm Snead to the Minnesota Vikings in early 1971, to leave the team a choice between journeyman Pete Liske and the raw Rick Arrington.