After unification of the East End and West End clubs, Newcastle United continued to play in East End's red until 1894 when they adopted the now iconic black and white striped shirts, with black shorts and socks to avoid frequent colour clashes.

Newcastle has a long-standing rivalry with neighbouring Sunderland with whom they have contested the Tyne-Wear derby since 1898.

The club are the current champions of the Football League Championship.

The club was founded in December 1892 by the merger of two local teams Newcastle East End and Newcastle West End who were previously rivals in the Northern League, but after West End fell into financial difficulties they decided to merge. The deal included the lease on West End's stadium St. James' Park and several names were suggested for the new club, including Newcastle Rangers and Newcastle City, however they chose the name Newcastle United.

Newcastle United went on to win the League Championship on three occasions during the 1900s; 1905, 1907 and 1909. The club's success continued in cup competitions, as they reached five FA Cup Finals in seven years, appearing in the final of 1905, 1906, 1908, 1910 and 1911. However they went on to win just one of them, the 1910 Final against Barnsley, in a replay at Goodison Park. However, there was still one particular low point during this period, as the team suffered a 9–1 defeat by fierce rivals Sunderland in the 1908–09 season, Sunderland still count the result as their record highest win.

The team returned to the FA Cup final in 1924, in only the second ever final at Wembley Stadium. They were successful in defeating Aston Villa and therefore winning the club's second FA Cup trophy in its history.

Newcastle won the League a fourth time in 1927, the last time they have to date. Notable players during this period include the likes captain Hughie Gallacher (the most prolific goals per game scorer in the club's history), Neil Harris, Stan Seymour and Frank Hudspeth.

During the 1950s, Newcastle won the FA Cup trophy on three occasions within a five year period. In 1951 they defeated Blackpool 2–0, a year later Arsenal were beaten 1–0 and in 1955 they defeated Manchester City 3–1. Newcastle had gained a high profile, and so had their players; 'Wor Jackie' Milburn and Bobby 'Dazzler' Mitchell in particular. Other players of this time were Frank Brennan (like Mitchell a Scot), Ivor Broadis, Len White and Welshman Ivor Allchurch.

The old war horse Joe Harvey, who had captained the team to much of their post-war success, returned to revitalise Newcastle. He teamed up with Stan Seymour to rebuild them and they won the Second Division Championship in 1965. Newcastle then became very much an unpredictable and inconsistent team, always capable of defeating the best, but never quite realising their potential.

Harvey's team qualified for Europe for the first time in 1968 and surprised many the following year by winning the Inter-Cities Fairs Cup, (which was the forerunner of the Europa League), beating Sporting Lisbon, Feyenoord, Real Zaragoza and Rangers along the way, before triumphing over two legs against Hungary's Újpest in the final. Newcastle possessed a reliable team and Newcastle's tradition of fielding a popular goalscorer at number 9 continued, as Welshman Wyn Davies was prominent.