Why do some individuals feel hostility and express bias against supporters of other political parties? Drawing on intergroup threat theory, we examine the role of emotions as a mechanism by which perceived threats against the ingroup are a source of increased affective polarization. In two survey experiments performed in the multiparty contexts of Sweden (N = 505) and Germany (N = 776), we manipulated intergroup threat using simulated online media, presenting participants with content related to immigration, and measured affective polarization using ratings of ingroup and outgroup supporter traits and feeling thermometers. Compared to a control condition, the threatening content evoked fear, anxiety, and anger among participants. However, only when individuals reacted to the threatening content with anger was increased affective polarization observed, in line with research showing that anger is a high‐arousal emotion related to an increased reliance on stereotypes. We conclude that individuals distance themselves from supporters of opposing political parties when they perceive a threat to their ingroup and subsequently react with anger. The findings contribute to the literature on affective polarization by stressing the role of emotional reactions to intergroup threat.