The rankings were released on Thursday following the conclusion of the Boxing Day Tests in Durban and Melbourne.
Smith, who last week won the Sir Garfield Sobers Trophy for the ICC Cricketer of the Year as well as the ICC Test Cricketer of the Year award, had entered the Melbourne Test in fourth position.
However, after scoring 134 not out and 70 not out, the 26-year-old has leapfrogged Kane Williamson of New Zealand, England’s Joe Root and AB de Villiers of South Africa into the top spot.
Ashwin, in contrast, has achieved the number-one spot for first time in his career after injury prevented Dale Steyn from bowling more than 3.5 overs in England’s second innings.
Even though the fast bowler bagged four wickets in the first innings, these were not enough for him to end the year as the number-one ranked bowler for the sixth time since 2009. Steyn had started the Durban Test leading Ashwin by four points and now trails the India off-spinner by the same margin.
In the ICC Player Rankings for Test Batsmen, Williamson, Root, de Villiers, Smith and David Warner had a chance to finish the year as the number-one ranked Test batsman after they were separated by 26 points in the lead up to the final Tests of the year.
While Williamson was busy in the ODI series against Sri Lanka, Root scored 24 and 73, de Villiers made 49 and 37 and Warner chipped in with 23 and 17.
Steve Smith, who was also named in the ICC Test and ODI Teams of the Year, is the third Australia batsman in the last decade after Ricky Ponting (2005 and 2006) and Michael Clarke (2012) to finish the year as the number-one ranked batsman.
Other batsmen since 2005 to finish the year as the top batsman are Kumar Sangakkara (2007, 2010 and 2011), Shivnarine Chanderpaul (2008), Gautam Gambhir (2009) and de Villiers (2013 and 2014).
Smith also finished 2015 as the leading run-scorer with 1,474 runs. This performance is clearly reflected in his ranking; he started the year in fifth position, achieved the number-one position for the first time after the Kingston Test against the West Indies in June, before finishing the year on top of the tree after hovering inside the top five in the last quarter of the year.
There was good news for Adam Voges, Dean Elgar, Usman Khawaja, Jonny Bairstow and James Taylor who have ended the year in their career-best rankings.
Voges scored 106 in his only innings at the MCG and has jumped up four places to 11th, Elgar has gained 12 places and is now in 28th position after scoring 118 not out and 40 in Durban, Khawaja has vaulted 11 places to 39th after scores of 144 and 56, Bairstow 41 and 79 have lifted him 13 places to 43rd and Taylor has stormed up 46 places to 61st after contributions of 70 and 42.
In the ICC Player Rankings for Test Bowlers, Ashwin has become the first India bowler since Bishen Bedi in 1973 to achieve the milestone of finishing the year in number-one Test position.
In fact, Bedi, an ICC Hall of Famer, is the only India bowler to ever top the Test bowling table, while Bhagwath Chandrasekhar, Kapil Dev and Anil Kumble peaked at number-two during their careers.
Ashwin has finished 2015 as the most successful bowler with 62 wickets in nine Tests, and this is reflected in his ranking after he started the year in 15th position and slowly but surely moved to the top of the chart.
In the past decade, Shane Warne has finished in the top position in 2005 and Muttiah Muralidaran completed a hat-trick from 2006 to 2008, before Steyn got his grip on the top spot which was only broken in 2013 when his team-mate Vernon Philander topped the table.
England’s Stuart Broad was the second leading wicket-taker in 2015 with 56 wickets in 14 Tests.
This includes five wickets in the Durban Test, which have proved to be the cornerstone of his career-high third position in the latest rankings.
Broad, who started the year in eighth position, has now become England’s highest-ranked bowler after James Anderson who has slipped to fifth after missing the Durban Test due to an injury.
Other bowlers to finish the year on career-high rankings include Nathan Lyon in 14th place (up by one), Moeen Ali in 23rd (up by seven places), Mitchell Marsh ion 52nd (up by nine places) and Dane Piedt in 59th (up by five places).
Ashwin, for the second time in three years, has finished as the number-one ranked Test all-rounder. Bangladesh’s Shakib Al Hasan had started 2015 as the top all-rounder.