[3] On 8 May 2018, the incumbent Labour MP Heidi Alexander announced her appointment as London Deputy Mayor for Transport, a role that required her to stand down from the House of Commons.

Through demographic modelling, the Remain vote in the Lewisham East constituency was estimated as 66% by Number Cruncher Politics and as 65% by Chris Hanretty at Royal Holloway.

They intended to use the by-election to "send a message to the Labour leadership about Brexit", with party leader Vince Cable aiming to "cut the majority substantially".

[2][28] The Lewisham East Labour Left caucus group called for a socialist MP who would "campaign for...a left-wing government with Jeremy Corbyn as Prime Minister".

[29] On 10 May 2018, Ian McKenzie, chair of the Constituency Labour Party (CLP), emailed members concerned that the National Executive Committee (NEC) was rushing the selection to prevent them having their say.

[2][30] Potential left-wing candidates included Sakina Sheikh, GMB trade union organiser Nadine Houghton, and NEC member Claudia Webbe.

[35] On 14 May the NEC announced a shortlist of Webbe, Dacres, Lewisham councillor Janet Daby and Sheikh,[36] all women from ethnic minorities.

[43] Sheikh was temporarily withdrawn from the ballot prior to the selection meeting, following accusations that she had supported a rival political organisation, but was reinstated minutes later.

[8][44] On 22 May, McKenzie, credited with having secured the Labour candidature for Daby which he claimed had "humiliated" Momentum and Unite, was suspended as chair of the CLP and is facing possible disciplinary action over tweets from 2015 and 2016 about Emily Thornberry and ISIS.

[46] The Liberal Democrats announced their opposition to plans by Lewisham Council to seize the land of Millwall FC's youth academy for redevelopment.

[51] On 12 June 2018, police shut down a by-election hustings in Catford, leading to one arrest, after it was disrupted by anti-racism protesters led by Stand Up to Racism and Lewisham Anti-Racist Action Group.

[56] The Liberal Democrat leader Vince Cable said: "This result sends a message to the Labour leadership that it cannot take pro-European voters for granted.