Niche parties often originate in social movements, yet the latter’s role in shaping these parties has received scant attention. I argue that movement roots can help niche parties achieve both vote- and policy-seeking goals by keeping core issues salient, bolstering issue ownership and securing allies in civil society. Employing interviews with movement, as well as Green and Pirate party leaders in Sweden and Germany, I identify three mechanisms (electoral pressure, grassroots linkage, elite orientation) that lead to programmatic alignment. This article extends an emerging research agenda that highlights how social movements shape party politics and offers evidence that niche party–movement interactions open new avenues for political representation counterbalancing mainstream parties’ increasing detachment from civil society.