Hu had favored his protege, Li, as his successor. Li, who belonged to Hu's Communist Youth League faction, instead got the No. 2 spot in the party hierarchy.
On Saturday, in a sign of a further consolidation of Xi's power, the party congress from the leadership, dropping him from the party's 205-member Central Committee. Li and two others who had also been appointed under Hu and were dropped from the committee are expected to go into retirement.
Hu left the meeting at the hulking Great Hall of the People not long after the election of the new Central Committee, and more than two hours after the session had started.
The spectacle was, in the words of longtime China watcher Bill Bishop, "humiliating."
The "image of Hu Jintao being led out is a perfect symbol of Xi's absolute decimation of the 'Communist Youth League' faction," Bishop wrote in his newsletter.
Another member of the same faction, Hu Chunhua, was denied a spot on the all-powerful Politburo Standing Committee in a leadership shuffle at the end of the congress, despite being an early favorite. Hu Chunhua didn't even make it onto the 24-member Politburo one rung below.
Xi has been steering China into what the party calls a "new era," away from the legacy of former leader Deng Xiaoping, who launched China on its economic rise with market-oriented reforms — and also selected Hu as a future leader.
It was Deng who put Hu on the all-powerful Politburo Standing Committee — from which China's leaders come — at the relatively tender age of 49.
Xi has broken with tradition by declining to consult with senior party officials such as Hu, or defer to their factional concerns, analysts say.
Hu attended the congress as a specially invited delegate, as is customary for senior retired officials. He was seated onstage next to Xi, in the front row with party leaders.
Whether he was able to take part in discussions isn't known — it's part of the secrecy that surrounds party events. Since stepping down from the presidency in 2013, he has rarely been seen in public, drawing additional attention to his sudden departure at the congress.