The former prime minister's role was made formal at the party's federal council meeting in Melbourne on Friday.
"I owe the Liberal Party big time and that's why I regard it as my duty to serve the party in this time of existential crisis," Mr Abbott told the gathering.
"As the last successful federal leader of the opposition, I do believe that I have the ability to help Angus Taylor to be the next successful federal leader of the opposition."
Mr Abbott led the coalition to a landslide election victory in 2013 before being replaced as leader two years later.
He said the country was drifting backwards, citing mass migration and what he called damaging taxes and an unnecessary focus on emissions reductions.
"We don't believe in ourselves anymore," Mr Abbott said.
"Our economy is stagnating, our society is fragmenting, our security is in peril, and underneath it all, there is a kind of spiritual malaise.
"I absolutely believe in the marrow of my being that we remain the best hope of better government in this country."
Outgoing president John Olsen said the party needed to face up to having delivered its worst federal election result and begin to rebuild its fortunes.
The ex-South Australian premier urged the party to rebuild and earn back the trust of Australians.
"It takes character to rebuild when the work is hard and the path is long; I look forward to seeing the party's fortunes restored," he told the council.
Mr Olsen said voters had taken note of the coalition's infighting, including temporary splits between the Liberals and Nationals, and Australians expected "confidence, conviction, and consistency".
"They expect us to focus on greater concerns than our internal disputes," he said.
Support for the federal Liberal Party has plummeted to historic lows as support for Pauline Hanson's One Nation rises.
The dire state of affairs and Opposition Leader Angus Taylor's attack on the Albanese government's controversial federal budget are hot topics at the council, which continues on Saturday.
The next Liberal leader up to bat at a major election, Victorian Opposition Leader Jess Wilson, vowed to rebuild her state, which she said had lost hope.
"We can win here in Victoria in November. We can win the next federal election," she said.
"The only way to remove Anthony Albanese is to vote Liberal."
Ms Wilson promised disciplined budgets and lower taxes through scrapping an Indigenous treaty, putting a freeze on public service hiring and capping public sector executive salaries.
"Taxes must always be lower under a Liberal government," she said.
She promised to be harder on crime, with jail time for those who broke bail and harsher punishments for juvenile offenders.
According to a Roy Morgan survey published on Tuesday, primary support for the coalition dropped one per cent to 23 per cent in the past week while support for One Nation increased by one per cent to 25.5 per cent.
Labor Party support fell two per cent to 27.5 per cent during the same period.
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