Arnold Cassola has resigned from Alternattiva Demokratika, a party which he co-founded and led for several years, amid differences over the topic of abortion.
He told Times of Malta, however, that he will contest the European Parliament elections as an independent candidate.
In a letter to chairperson Carmel Cacopardo, Prof Cassola said that there were clearly differences between him and the party's executive over abortion.
He said he was strongly against abortion except where the life and health of the mother were in danger.
On Friday, AD's MEP candidate Mina Tolu said that political parties' refusal to discuss abortion and reproductive rights was "frightening and unacceptable".
Prof. Cassola had called on the party to dissociate itself from her comments and to reaffirm a position against abortion. This, he said, was a red line for him.
Mr Cacopardo had replied that AD had no position on abortion and the party executive would discuss Prof. Cassola's request at its next meeting.
Prof. Cassola in his resignation letter said it would be better for AD to be free to take its decisions without hindrance from his 'minority position'.
He said he was therefore, with regret, resigning from AD after 30 years of service but he would continue to militate on his own.
In a reaction to the resignation letter, AD secretary Ralph Cassar told Prof. Cassola that it would have been better had he awaited the internal discussion instead of publishing his resignation letter.
He confirmed that the party had no position on abortion but said that Prof Cassola's comment that he was against abortion except where the life and health of the mother were in danger was effectively a proposal which should be discussed.
He said he would welcome his input to the discussion.
Prof. Cassola was among the founders of AD in 1989 and secretary general of the European Greens Party between 1999 and 2006. He was a member of the Italian Parliament between 2006 and 2008.
In the 2004 election for the European Parliament he obtained 9.33% (or 23,000 votes) of the first-preference votes, just failing to be elected one of Malta's five MEPs.