"We assess Russian President Vladimir Putin ordered an influence campaign in 2016 aimed at the US presidential election," the report said. "We further assess Putin and the Russian government developed a clear preference for President-elect Trump. We have high confidence in these judgments."
The aim was to undermine the public's faith in the democratic process and in Clinton's campaign, Reuters reported.
US intelligence agencies believe Russian military intelligence, the GRU, worked through WikiLeaks, DCLeaks.com and the Guccifer 2.0 "persona" to release emails of the Democratic National Committee (DNC) and other top Democrats.
"When it appeared to Moscow that Secretary Clinton was likely to win the election, the Russian influence campaign began to focus more on undermining her future presidency," the report said.
The leaked emails received abundant media coverage during the election campaign and led to the resignation of the DNC's chief.
However, the report doesn't go into detail of how the Russians gave their information to WikiLeaks and others.
According to Reuters, WikiLeaks founder Julian Assange has said he didn't receive the emails from "a state party".
Nothing in today's declassified ODNI report alters our conclusion that WikiLeaks' US election related sources are not state parties.— WikiLeaks (@wikileaks) January 7, 2017
The report, which was produced by the Central Intelligence Agency, the Federal Bureau of Investigation and the National Security Agency, did not go into detail of how the Russian meddling impacted the election nor did it give any details or evidence to back up its conclusions.
It also found Russians did not target US systems involved in tallying votes.
Russia has denied the allegations.
After receiving a nearly two-hour briefing of the report yesterday, President-elect Trump defended his victory and blamed the DNC for allowing itself to be hacked. The report, however, states the cyber attacks were conducted on both the Democratic and Republican parties.
Gross negligence by the Democratic National Committee allowed hacking to take place.The Republican National Committee had strong defense!— Donald J. Trump (@realDonaldTrump) January 7, 2017
Trump is set to take office on 20 January after he won the backing of the electoral collage.