Mr Sanders, 78, told his campaign staff about his decision on a
conference call on Wednesday. He is expected to address his supporters
online shortly.
A self-described Democratic socialist, Mr Sanders
found early success making healthcare and working-class issues a key
part of his election platform.
For a long time the front runner, he has slipped behind Mr Biden in the party's primaries in recent weeks.
Mr Sanders had pursued the presidential nomination before, losing out in 2016 to Hillary Clinton.
https://www.bbc.com/news/world-us-canada-52219756