Edwards says Clinton and Obama had both pledged that "they will make ending poverty central to their campaign for the presidency."
Edwards says that on his way to make his campaign-ending statement, he drove by a highway underpass where several homeless people live. He said he stopped to talk, and as he was leaving, one of them asked him never to forget them and their plight.
The former North Carolina senator did not immediately endorse either Clinton, seeking to become the first female president, or Obama, the strongest black candidate in history.
Both of them praised Edwards -- and immediately began courting his supporters.
The impact of Edwards' decision will be felt in one week's time, when Democrats hold primaries and caucuses across 22 states, with 1,681 delegates at stake.