Justice Hansen is a High Court Judge in his native New Zealand and is New Zealand Cricket's appointment on the International Cricket Council's (ICC) Code of Conduct Commission.
Singh was punished with a three-match ban after the commission upheld a complaint from Australian skipper Ricky Ponting that Singh insulted Australian all-rounder Andrew Symonds by calling him a monkey.
The finding and sanction enraged the Indian tourists who were already upset by several umpiring decisions that went again them in the Test which they narrowly lost to go two down in the four Test series.
The Indians briefly suspended all travel on their tour prompting the ICC to stand down umpire Steve Bucknor, who had been the main target of the Indian anger.
The ICC said it had received official notification of the appeal from the Board of Control for Cricket in India (BCCI) on Monday and appointed Justice Hansen in line with ICC Code of Conduct processes.
No time, date or venue for the appeal have yet been fixed, but the process indicates that the appeal should be heard within seven days of the commissioner being appointed. This time period may be extended if circumstances dictate.
In the meantime, Harbhajan may continue to play pending the verdict of the appeal being given. The BCCI announced late Tuesday that the tour in Australia would go ahead.