Birth of West Ham United

The reborn club continued to play their games at the Memorial Ground in Plaistow (funded by Arnold Hills) but moved to a pitch in the Upton Park area when the team officially severed ties with the company (losing their works provisioned offices in the process). After being made groundless in 1901 the team became transient, playing their home games on a number of local teams' grounds until moving to its current home, Upton Park (in the guise of the Boleyn Ground stadium), in 1904.

West Ham's first game in their new home was against fierce rivals Millwall (themselves an Ironworks team, albeit for a rival company) drawing a crowd of 10,000 and with West Ham running out 3–0 winners,and as the Daily Mirror wrote on 2 September 1904:

West Ham Utd had joined the Western League for the 1901 season in addition to continuing playing in the Southern Division 1. In 1907 West Ham were crowned the Western League Division 1B Champions, and then defeated 1A champions Fulham 1–0 to become the Western Leagues Overall Champions.
In 1919, still under King's leadership, West Ham gained entrance to the Football League Second Division, the first game being a 1–1 draw with Lincoln City, and were promoted to Division One in 1923, also making the first ever FA Cup Final to be held at the old Wembley stadium. Their opponents were Bolton Wanderers. This was also known as the White Horse Final. This is because so many people turned up to the game, (estimated at 200,000), that they spilled out on to the pitch. The pitch had to be cleared prior to kick-off, by Billie, a giant white horse (actually grey) being ridden by PC George Scorey. The Cup Final match itself ended 2–0 to Bolton Wanderers. The team enjoyed mixed success in Division 1 but retained their status for 10 years and reached the FA Cup semi-final in 1927.

In 1932 the club was relegated to Division Two and long term custodian Syd King was sacked after serving the club in the role of Manager for 32 years, and as a player from 1899 to 1903. He was replaced with his assistant manager Charlie Paynter who himself had been with West Ham in a number of roles since 1897 and who went on to serve the team in this role until 1950 for a total of 480 games.

The club spent most of the next 30 years in this division, first under Paynter and then later under the leadership of former player Ted Fenton. Fenton succeeded in getting the club once again promoted to the top level of English football in 1958 and in helping develop both the initial batch of future West Ham stars and West Ham's approach to the game.