[2] In the 1970s, he was active in Dash and was a fierce opponent of the coalition with Begin and his right-wing Likud party in 1977.

In 1996 he also ran in the primaries for the Labor Party, where he later served as the influential chairman of its legal committee until he resigned in 2004, after his name came up as a candidate for the Supreme Court.

On 24 June 2007 he was selected by the Judicial Committee to serve as a judge on the Supreme Court.

His appointment was historical because it was the first time in decades that a lawyer from the private sector was chosen,[3] and it was part of the judicial shakeup initiated by Justice Minister Daniel Friedmann.

Melcer was part of the decision by the Supreme Court in 2009 to order the government to demolish illegally built Palestinian homes in the West Bank.