Bueltmann is vocal in her support for Britain remaining in the European Union.[17] As her research is focused on migration history, and she is a German living in the UK, her concern about Brexit is both professional and personal.[18] She was a member of the lobbying group "Historians for Britain in Europe" and describes herself as an EU citizen.[19][20] Before the referendum, Bueltmann voiced concerns that the "tolerant UK I love seems to be vanishing".[21][22][23] After becoming a public figure for the Remain movement, she received abusive messages.[24][25] She was not surprised by the outcome of the EU referendum, but, as many others, has been troubled by the events since.[26]
In March 2017 she attended Newcastle's pro-EU rally, and, when interviewed by the BBC, said she had moved from Germany to "contribute to life and society in the UK and I think I've been doing that every single day since I arrived eight years ago".[27] She was a guest speaker at the People's March for Europe in London in September 2017.[28] Since Britain's vote to leave the EU, she has written articles for a number of newspapers and online platforms, including The Guardian,[29] HuffPost UK,[30] and Metro.[31]
Bueltmann has publicly spoken out against the government's Brexit reassurances.[32] She remains concerned about the rights of EU citizens in the UK, and Britons who live in the EU, and continues to take a vocal stand against their being used as bargaining chips in negotiations.[33] When the government made a plea for EU academics to remain in the UK, Bueltmann told The Independent newspaper: "if they really meant they want us to stay, they would have guaranteed our rights fully on 24 June 2016".[34] She later argued in the Times Higher Education, in a rebuttal to the then Immigration Minister Brandon Lewis's article addressed to EU nationals working in Higher Education,[35] that what everyone failed to see was that the UK is not the destination for EU nationals, but their home.[36]
Since the EU referendum Bueltmann has focused primarily on the situation of the more than three million EU citizens at home in the UK and fighting for the protection of their rights. She is working with other campaigners, politicians and policy organisations, including the German Friedrich-Ebert-Stiftung.[37]
In July 2018, Bueltmann founded the EU Citizens' Champion campaign to facilitate that work. The campaign serves two purposes: to support the3million, the UK's leading not for profit organisation working to protect EU citizens’ rights, with a fundraiser, and to facilitate engagement activities that help change the narrative about freedom of movement and migration.[38] The campaign launch video - a satire on settled status - features actor and director David Schneider.