The experienced Hohns, who previously served as chief selector during a hugely successful period for Australia, currently sits on the four-man selection panel with Mark Waugh, coach Darren Lehmann, and now Chappell.
Cricket Australia chairman David Peever said Hohns had agreed to step up to ensure continuity while the search for a full-time replacement was carried out.
"It is vital that Australian cricket finds the best candidate for this role," said Peever.
"Trevor is highly experienced as a selector, and will ensure we place our best players on the field this summer while we seek a permanent replacement for Rod."
Former Test fast bowler Jason Gillespie and ex-captains Ricky Ponting and Steve Waugh have all been touted as possible successors to Marsh.
The retired wicketkeeper resigned yesterday with immediate effect after a run of five heavy Test defeats left the team humiliated and facing demands for heads to roll.
They crashed to a third-straight home series defeat to South Africa on Tuesday and now face being whitewashed in a home series for the first time in their history if they lose to the Proteas in Adelaide next week.
The last time Australia lost six straight Tests -- against India and England in 2013 -- the coach at the time, Mickey Arthur, was sacked.
While spinner Hohns played only seven Tests for Australia, he had a highly successful previous stint as a national selector from 1993 to 2006, including a decade as chairman.
Under his guidance, Australia won a record 16 successive Test matches and claimed the 1999 and 2003 World Cups in a golden era. He rejoined the selection panel in 2014.
He will be aided in trying to turn around the team's fortunes by former Test captain Chappell, who has been drafted in on a temporary basis ahead of a raft of changes expected for Adelaide.
Lehmann has declared that only four players -- captain Steve Smith, David Warner, Mitchell Starc and Josh Hazlewood -- were sure to keep their places after Australia's second demoralising collapse in the Hobart Test this week.
Peever said Chappell, who has had two previous stints as a selector, had been instrumental in restructuring Cricket Australia's youth pathway programme and had his finger on the pulse of young talent.
"His in-depth knowledge of up-and-coming talent in the Australian system will be invaluable," he said.
"Naturally the board and our senior executive are disappointed with the recent Test performances," Peever added.
"But we have every confidence that all those involved, including our coaching staff and team management, will do their utmost to turn that around."
Australia's team announcement for next week's third and final day-night Test has been delayed until Sunday so selectors can assess players' form in domestic Sheffield Shield matches.
Mark Waugh said selectors may need to use their "gut instinct" when they finalise the batting order due to a lack of clear-cut contenders.
"Obviously there will be changes at Adelaide. I can't say how many or who at this present point in time," Waugh said.
"But I can assure you we are looking at a lot of batsmen.
And if someone sticks their hands up and gets a 150 or a 100 in this (Shield) round then it is really important.