Prof Rodney Smith, from the department of government at the University of Sydney, said Friday's resignation was "likely both to weaken the National Party but will also make National Party MPs a little bit resentful because of the fact that the prime minister did come out so openly and criticise Joyce and tell him to consider his position".
The spokesman said Mr Joyce, 50, made no accommodation expense claim until January 3 and no travel claim was made for Ms Campion.
He stated that resigning will be a "circuit breaker for Vikki, a circuit breaker for my unborn child and my daughters".
The next Nationals leader will be chosen at a party room meeting on Monday.
Joyce and Turnbull have openly attacked each other since news of the deputy prime minister's office affair broke.
He said: "This is never about me".
The issue has dominated headlines in Australian media this month, taking the spotlight away from the prime minister's policy agenda, including his bid to legislate corporate and personal tax cuts.
Joyce has described the allegation as defamatory, denies them, and called for the matter to be referred to police.
Labor frontbencher Anthony Albanese again called for Joyce to resign, criticising his decision to do media interviews during a week of leave.
"This has got to stop, it's not fair on them, it's just completely and utterly unwarranted".
Speaking outside the White House in Washington, DC, Mr Turnbull repeatedly dodged questions about whether he wanted Mr Joyce to remain as the Nationals leader.
His Nationals colleague, Victorian MP Andrew Broad, says he will move a resolution to oust Mr Joyce as party leader on Monday.
NSW MP David Gillespie confirmed on Friday to Radio 2GB he will also be a candidate for leader, while Queensland MP David Littleproud, who was controversially promoted to cabinet by Mr Joyce ahead of Mr Chester just over two ago, has also been discussed for leadership positions.
Moving back to the bench, he will continue to be a part of the parliament. He will remain in parliament, safeguarding Turnbull's shaky one-seat majority.
"On any measure The Nationals team in Government has delivered for the people in rural and regional Australia who we have represented for almost 100 years".
Joyce's resignation comes a week after Turnbull savaged his deputy in a news conference, calling his affair with Campion a "shocking error of judgment".
Prime Minister Malcolm Turnbull issued a statement shortly after Joyce announced his decision, thanking him for being a "a fierce advocate for rural and regional Australia", BBC reported. Mr Joyce and Vikki Campion are now expecting a baby in April.
Speaking in Washington while on an official U.S. visit, Mr Turnbull declined the opportunity to throw his support behind his coalition partner, insisting the decision was a matter for the Nationals.