Before 1945 the Dagenham area was part of
the Romford constituency. The MP for the latter seat since 1935, Labour's
John Parker, continued to represent Dagenham until 1983. Parker was the last serving MP to have been elected before the Second World War, and with 48 years in Parliament, was the longest-serving Labour MP in history, a record he held until December 2017. The seat was first contested in the
2010 general election which resulted from the
Boundary Commission's report that recommended merging the majority of the former constituencies of
Dagenham and
Hornchurch and added to existing
electoral wards a small part of River ward was also transferred from
Barking. In 2010 Labour's
Jon Cruddas took the seat gaining a
marginal 5.9% win, facing a strong nominal (ward-by-ward) Lab–Con
swing measured against the previous forerunner seats and candidates.
BNP candidate Michael Barnbrook came third with 11.2% of the vote, his party's second-best showing in the election. In 2015, Cruddas, incumbent won an 11.6% majority; the runner-up party changed to being
UKIP closely followed by the Conservative candidate. In 2019, Cruddas' majority was cut to just 293 votes, the lowest Labour majority in Dagenham ever, which has been represented by Labour MPs since 1945. The electoral wards in both boroughs were redrawn in 2022 and subsequently the constituency no longer aligns with ward boundaries. ==Boundaries==