Flynn was a close adviser to Trump during the campaign - and famously led a "lock her up" Hillary Clinton chant at the Republican National Convention.
A former member of Trump's inner circle, Cohen has been co-operating with Special Counsel Robert Mueller's investigation into Russian interference in the 2016 U.S. election and possible co-ordination with the Trump campaign.
Flynn is scheduled to be sentenced December 18 by federal Judge Emmet Sullivan in DC federal court.
Mueller had to file his recommendation for sentence before a midnight deadline on Tuesday.
Flynn was forced out of his post as national security adviser a year ago after officials said he misled Administration officials, including Vice-President Mike Pence, about his contacts with Sergey Kislyak, Russia's ambassador to the United States at the time. In late 2016, the two allegedly spoke about the US sanctions imposed on Russian Federation. He has admitted he lied to Congress to help Trump and broke campaign finance laws by helping to arrange hush money for women who might have embarrassed Trump with accusations of infidelity as he was running for president. Flynn was under investigation by the Justice Department for the work when he became national security adviser.
The special counsel Robert Mueller's office has reportedly told defence lawyers it is "tying up loose ends" in the Russian Federation investigation, signalling that the inquiry is coming to a close.
Questions also have been raised about the Flynn plea itself, considering a congressional Republican report earlier this year claimed fired Federal Bureau of Investigation boss James Comey once testified that Federal Bureau of Investigation agents did not think Flynn intentionally lied.
"Given the defendant's substantial assistance and other considerations set forth below, a sentence at the low end of the guideline range - including a sentence that does not impose a term of incarceration - is appropriate and warranted", the memo says.
An attorney for Flynn and a spokesperson for the special counsel declined to comment.
Cohen, once Trump's self-described "fixer", said in a court filing last week that he had pursued a Moscow building project with Russian government officials well into the presidential campaign, with Trump's knowledge. As part of his plea agreement, Flynn agreed to cooperate with the Mueller investigation.
Whatever it is that Flynn said, it's clear that Mueller liked it.
Former FBI Director Robert Mueller, the special counsel probing Russian interference in the 2016 election, departs Capitol Hill following a closed door meeting, June 21, 2017. Manafort was convicted on multiple counts of financial fraud over the summer in connection with work he completed in Ukraine as a political consultant.
He has told friends that he is mystified that he is taking the fall for actions he carried out on behalf of Trump, who remains unscathed.