Australia reclaim top Test rank
Australia's Steven Smith (L) and Brad Haddin (R) celebrate their 5-0 victory in the Ashes against England at the Sydney Cricket Ground on January 5, 2014 - by Saeed Khan
They also remain the top-rated one day international side in the latest official rankings from the International Cricket Council (ICC).
It is the first time since December 2008 that the country has been ranked number one in Tests and ODIs at the same time. They last held the top Test ranking in August 2009, when they were displaced after losing the Ashes 2-1 to England.
Darren Lehmann's Australians nudged out South Africa, who had held the top Test spot since August 2012 following their Ashes whitewash of England and a series defeat of the Proteas.
Australia gained eight ratings points to move up from 115 to 123 points to be equal with South Africa, who dropped from 127, but Australia moved ahead by a fraction of a point.
England are currently third, ahead of Pakistan and India.
Clarke said Australia's ascension was the highlight of his decorated career.
"I don't think I have had a more satisfying day or feeling in my career," he said.
"For me, as captain, No.1 was my goal. I said from day one -- I think we were third or fourth when I took over from Ricky (Ponting) -- and then I know we got to fifth after losing in India.
"My goal never changed, I wanted to help this team get back to being the No.1 team in the world and I know the players were exactly the same."
Clarke said achieving the top Test spot was more satisfying than the one-day mantle because they had got there from such a low ebb, including being labelled the worst Australian team ever to tour India after plummeting to a 4-0 defeat there early last year.
"We are incredibly proud to be the number-one ranked team in the world in both Test and ODI cricket, which are two of the team's most important goals," he said.
"There has been an enormous amount of hard work and effort on and off the field that has led to this result.
"However, the true test of a great side is sustained success and now our goal is to maintain these rankings and continue to play great cricket as we lead into challenging Test series against Pakistan and India, and the ICC Cricket World Cup at home."
Lehmann has turned around the fortunes of the Australian Test and one-day sides following a tumultuous period in which coach Mickey Arthur was sacked.
After losing the 2013 Ashes series 3-0 in England, Australia swept their return home series against England 5-0 during the last southern summer.
They then scored an impressive 2-1 away series win over South Africa.
Cricket Australia chief executive James Sutherland said they planned to remain on top for years to come.
"We believe we are putting in place the foundations to make that happen. We are committed to doing everything we can to achieve continuous improvement," he said.
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