Former Relate counsellor Gary McFarlane, who was sacked after refusing to give sex therapy to same-sex couples, said the judgment by the European Court of Human Rights against him was "regrettable".
Speaking in central London, he said he would appeal the decision while continuing to counsel same-sex couples in other aspects of their lives.
The ECHR's ruling found against Mr McFarlane on the grounds that he took on the role at Relate in the knowledge that clients could not be divided up in accordance with their sexual orientation.
It concluded the company's action was designed to enable it to provide a service without discrimination.
Barrister Adam Wagner, who specialises in human rights, has confirmed the timeline for the three Christians who lost their cases at the European Court of Human Rights to appeal to the Strasbourg court's higher chamber.
While cross-wearing BA employee Nadia Eweida enjoyed victory at the European Court of Human Rights (ECHR), three other Christians lost their cases, including hospital nurse Shirley Chaplin, who had been prevented from wearing a cross visibly around her neck.
They will be appealing today's judgment at the ECHR's Grand Chamber.
Speaking at a news conference in central London, Ms Chaplin said she was "very disappointed" by the judgment but heartened that other Christians can now wear a cross in the workplace.
She said she still feels that other religions are given more freedom in the workplace and called upon David Cameron to live up to a promise to change the law to protect cross-wearers.
The European Court of Human Rights has deemed a fair balance was not struck between British Airways check-in clerk Nadia Eweida's desire to demonstrate her religious belief with a "discreet" cross and the airline's wish to "project a certain corporate image".
The judgment, published in Strasbourg, found the airline's aim was "undoubtedly legitimate" but said British courts had accorded it "too much weight" in previous rulings.
Barrister Adam Wagner, who specialises in human rights, has tweeted that today's judgment by the European Court of Human Rights could benefit religious believers in the workplace: