The 50,000 euro ($65,000) prize is awarded every year by the European Parliament to honor defenders of human rights and freedom of expression.
Pakistani education activist and Nobel Peace Prize nominee Malala Yousafzai is widely regarded as the favorite when the prize is announced on 10 October.
She has been backed by the Alliance of Liberals and Democrats for Europe (ALDE), the Socialists & Democrats (S&D), and two center-right groups, the European People's Party (EPP) and the European Conservatives and Reformists Group (ECR).
Snowden, who fled the United States after disclosing classified electronic-surveillance activities, is supported by the Greens and the leftist GUE/NGL but remains a controversial choice for most members of the European Parliament.
Byalyatski, Lobau, and Statkevich enjoy strong Polish backing in the chamber and are nominated on behalf of all Belarusian political prisoners.