Gillingham became founder members of the football leagues third division in 1920. In the year 1964, Gillingham gained promotion in to the third division by winning the fourth division title on goal difference to Carlisle. It was during that period they enjoyed a 52 match league and cup unbeaten run that spanned between April 1963 and April 1965. The Gills were relegated back to the fourth division in 1971 and found promotion again in 1974. They settled in the third division for the next fourteen years and reached the top five of the third division for three years running between 1985 and 1987 under the guidance of Keith Peacock.
Gillingham improved during the 1990’s and for the first time gained promotion in to the second tier of English football, however they could not sustain that position and suffered relegation in to the ‘league one’ at the end of the 2005 – 2006 campaign.