The club traces its roots back to 1877. The club was formed as Thornhill Football Club (later Thornhill United). For many years the leading team in the area was Rotherham Town F.C., who spent three seasons in the Football League while Thornhill United were still playing in the Sheffield & Hallamshire League. By the turn of the century, however, Rotherham Town had resigned from the Football League and gone out of business; a new club of the same name later joined the Midland League. Meanwhile, Thornhill's fortunes were on the rise to the extent that in 1905 they laid claim to being the pre-eminent club in the town and changed their name to Rotherham County For a period both clubs competed in the Midland League, finishing first and second in 1911-12. When the Great War ended, it was decided to extend The Football League by creating four new places in Division Two. Rotherham County, who had been champions of the Midland League in 1915 before the competition was suspended, were elected to one of the vacancies.
The Second Division was rather too tough for the Yorkshire side and in 1923 they were relegated to Division Three (North). In 1925 the club finished bottom and had to apply for re-election. Rotherham Town were themselves struggling and it was clear that to have two professional clubs in the town was not sustainable. Talks had begun in February 1925 and in early May the two clubs merged to form Rotherham United. Days later the reformed club was formally re-elected under its new name.
In a new amber and black strip, United may have begun with optimism but the new club fared little better than the old one. The now familiar red and white was adopted around 1928 but there was no improvement in the club's fortunes: in 1931 they again had to apply for re-election. Immediately after the Second World War things looked up. After adopting Arsenal-style white sleeved shirts, United finished as runners-up three time in succession between 1947 and 1949 and then were champions of Division Three (North) in 1951.
Rotherham reached their highest ever league position of third in the Football League Second Division in 1955, when only goal average denied them a place in the top flight after they finished level on points with champions Birmingham City and runners-up Luton Town.
The club held on to its place in Division Two until 1968 and then went into a decline that took them down to Division Four in 1973. In 1975 they were promoted back to the Third Division winning the championship.
The Millers won the division three title in 1981. Not only did the Millers pip one of their neighbours, Barnsley, to the championship but the double they recorded over Sheffield United helped send them tumbling into the fourth division.
In 1981-82, Rotherham were once again in contention for promotion to the top flight but eventually finished 7th, some 4 points off 3rd place. After a poor start the club had occupied a relegation place at the end of January before embarking on a club record winning spree of nine games which saw them rapidly climb the table.
The highlights of this campaign were undoubtedly their two meetings with Chelsea. Firstly the Millers thrashed the Londoners 6-0 at Millmoor before triumphing 4-1 at Stamford Bridge in the return in front of just 11,900 fans.
This exciting but ageing team, which included the attacking talents of John Seasman, Tony Towner, Rodney Fern and Ronnie Moore could not maintain this level of performance, however, although it was something of a surprise to see them relegated again the very next year.
By 1988, United were again in Division Four but won the Division title at the first attempt.
During the 1990s Rotherham were promoted and relegated between the Football League's lowest two divisions with some regularity. However in 1996, Rotherham made their first trip to Wembley, beating Shrewsbury 2-1 to win the Football League Trophy.
The most successful manager to take charge of Rotherham United in recent years is Ronnie Moore, a former player of the club. His first season ended in a mid-table finish and his second in a playoff defeat, but it was third time lucky in 1999-2000 when Rotherham finished as Division Three runners-up and gained promotion to Division Two. They were favourites to be relegated in 2000-01, but surprised many by finishing runners-up in Division Two and gaining a second successive promotion. During this highly successful campaign, Rotherham also comfortably beat Premiership side Southampton in the FA Cup.
Rotherham remained in Division One for four seasons, their most successful of which was the 2002–03 campaign. The Millers were in contention for a play-off place, but dropped off near the season's end to finish 15th, their lowest position all season. The following season the Millers sold Alan Lee to Cardiff City and struggled without the Irish international's goals, finishing 17th. A highlight of the season was a 1–1 draw with Arsenal in the League Cup. The 2004-05 season was worse still, and finally Rotherham were relegated. Ronnie Moore resigned during the relegation campaign, which saw Rotherham at the foot of the division for almost the whole season.
Mick Harford took over as Millers manager but was sacked after a run of 17 games without a win, to be replaced by Alan Knill. Early in 2006 it was announced that the club faced an uncertain future unless a funding gap in the region of £140,000 per month could be plugged. The problem was compounded as Rotherham had already sold their ground to Ken Booth in return for clearing £3m of debt and had no tangible assets, so administration was not a viable option. This led to the launch of a "Save Our Millers" campaign, aiming to raise the £1m needed to complete the season. It was also estimated that another £1m was required to complete work on the new stand. South Yorkshire neighbours Sheffield United offered their support by paying the wages of Stephen Quinn and Jonathan Forte during their loan spells at Millmoor, and also donated profits from the beam-back of the Sheffield derby. Many local clubs also held collections.
An eleventh hour intervention by a consortium of local businessmen offering substantial investment and a new business plan averted a possible dissolution of the club. Dennis Coleman took over as Rotherham United chairman, and made an immediate positive impact.
The final match of the 2005-06 season, home to MK Dons, was a winner-take-all relegation showdown. A scoreless draw, combined with a Hartlepool United draw with Port Vale, kept Rotherham up and consigned both MK Dons and Hartlepool to the drop. However, Rotherham were to start the following season with a penalty of minus 10 points as a result of their financial troubles.
Rotherham United began their second successive year in League One with a 10-point deficit as a result of the CVA which saved the club from liquidation. At one point during the close season, the team had only seven full-time professionals on the books but Knill made a number of signings during this period to bolster the squad including former Liverpool winger Richie Partridge, ex-Premiership players Delroy Facey and Martin Woods, former Bayern Munich and Nottingham Forest star Eugen Bopp and many others who have played at a higher level.
On 16 September, after three wins and two draws in their first nine games, Rotherham gained their first point in the league. They moved off the bottom of the table on 14 October, and after a run of three successive victories they moved out of the relegation zone after a 5-1 win against Crewe Alexandra on 28 October. After winning every league game in October, Knill was awarded the Manager of the Month and Yorkshire Manager of the Year awards.
At the arrival of the January transfer window, Knill sold stars Lee Williamson and Will Hoskins to Premiership side Watford for a combined fee in the ranges of £1.2 million. However, losing their two best players undoubtedly took its toll on the Millers, who sunk back to the bottom of the table after winning only one match in three months. By the end of February, the Millers sat 13 points adrift of safety, making the threat of relegation almost inevitable. This resulted in Knill being sacked on March 1, with Mark Robins becoming caretaker manager. Robins's position was made permanent on 6 April 2007, but he was not able to save Rotherham from relegation.
The Millers spent the majority of the 2007–08 season in the automatic promotion places, winning eight consecutive league matches towards the end of the year. However, in mid-March 2008 it was revealed that Rotherham had again entered administration and would be deducted 10 points. This was a accompanied by a drop in form and Rotherham finished ninth in the league. Towards the end of the season, it was revealed that local businessman Tony Stewart was to take over as Chairman and Club Owner, but was advised not to exit administration via a CVA, meaning an additional points deduction for the following season.
On 6 August, just three days before the start of the season, the Football League threatened to block Rotherham (as well as Bournemouth) from participating in League Two for the 2008-09 season, because the club had not yet exited administration or completed the process of transferring ownership. The Football League ruled that accepting the 17-point deduction would be a condition the team must obey to be eligible to play, which was accepted.
In addition, Rotherham United were forced to leave Millmoor, their home of over 100 years, after disputes with the landlords. Being further into debt, Rotherham also sold their training ground at Hooten Roberts and now train at Doncaster Rovers' Keepmoat Stadium renting out one of their pitches.
This led to further complications after the Football League demanded a £750,000 bond for the team to play outside of the Town's boundaries for a maximum of four years. The club must move back to Rotherham within this time period, or face losing their Football League share.
Under the new ownership of Tony Stewart, Rotherham kicked off their first game of the 2008–09 season at the Don Valley Stadium in Sheffield, with a 17-point penalty. Despite the odds, the Millers had an impressive season under the new regime, quickly wiping out the point deficit and being in contention for a play-off place until very late in the season. They also had two very impressive cup runs, comfortably beating League One Champions Leicester City and Champions of the Football League Championship, Wolverhampton Wanderers. This run also included beating local rivals Sheffield Wednesday on penalties and the thrashing of Leeds United. Without the controversial points penalty imposed by the football league, Rotherham would have finished 5th in the league.