At the party's presidential nominating convention that year, superdelegates - elected officials and other party leaders and activists - were able to add their influential votes to those coming from individual states' primary contests.
Supporters of left-leaning senator Bernie Sanders complained bitterly that superdelegates, unbound by state-level results and so not necessarily reflecting the popular will, threw the nomination to the more establishment candidate, Hillary Clinton. Even without the superdelegates' votes, Clinton won the majority needed for nomination. But Sanders supporters said the superdelegates' influence had unfairly made Clinton's candidacy appear unassailable. She went on to lose to Donald Trump in a stunning upset.
DNC members in a voice vote stripped superdelegates of the ability in future to cast polls during the first round of balloting, which has nearly always been decisive.
They will retain voting privileges on other Democratic business, such as the party platform.
In a Twitter message, Sanders welcomed the DNC's decision as "an important step forward in making the Democratic Party more open, democratic and responsive to the input of ordinary Americans."
Many superdelegates strongly opposed the change, saying the party activists who worked hardest to boost Democratic causes deserved special consideration.
But DNC chair Tom Perez defended it as a major reform that will "help grow our party, unite Democrats and restore voters' trust by making our 2020 nominating process the most inclusive and transparent in our history."