On 16 June, the club was promoted to the 2020–21 Bundesliga, returning to Germany's top tier for the first time since 2008–09.

[7][8] Bielefeld picked up 10 points from their next 4 league games before, their unbeaten run was broken with a 1–0 defeat at home to VfB Stuttgart, with a 91st minute Hamadi Al Ghaddioui strike consigning Arminia Bielefeld to their first league defeat of the season.

[10] Following a draw at home to Hamburger SV,[11] They won their next three league games against Dynamo Dresden, Holstein Kiel and 1.

[15] During the January transfer window, Bielefeld signed goalkeeper Oscar Linnér from AIK Fotboll[16] and young forward Sebastian Müller from 1.

[18][19] Bielefeld scored 10 goals in their following two games, recording a 6–0 win at home to Jahn Regensburg with six different goalscorers,[20] followed by a 4–2 victory away at Greuther Fürth.

[22][23] Despite going 1–0 down to 2nd placed VfB Stuttgart, a left-footed goal from Cebio Soukou in the 76th minute ensured Bielefeld retain their 6-point league at the top of the 2.

Bundesliga season was postponed later in March due to fears over the COVID-19 pandemic, leaving Bielefeld's chances of promotion in doubt.

[31][32] As of 31 January 2020[33] Note: Flags indicate national team as defined under FIFA eligibility rules; some limited exceptions apply.