Ireland's representative on the European Court of First Instance, John D. Cooke, has resigned shortly after beginning a second term at Europe's second-highest court.

Mr Cooke is best known for drafting the court's landmark judgment on Microsoft last year, which found the US software firm had abused its dominant position in the operating system market.

The ruling, which was made by a 13-judge panel at the Luxembourg court, forced Microsoft to pay a record €497 million fine, and set important precedents in EU competition law that could make life more difficult for dominant firms, particularly in the technology sector.

A court spokesman said yesterday that Mr Cooke had decided to retire and would leave the court in September, which is exactly 12 months after the Microsoft decision. "He intends to leave in September by which time the Irish Government will have to nominate a new judge. He wants to spend more time with his family in Ireland," he said.

Mr Cooke completed his first six-year term at the Court of First Instance - Europe's main court of appeal for competition cases - shortly before giving judgment in the Microsoft case. At 63 years of age, he was generally expected to complete a second term at the Luxembourg-based court.

"It's a shock," said Denis Waelbroeck of the Ashurst law firm in Brussels, who argued a case this week about pesticides before a three-judge panel including Mr Cooke. "I didn't think he would leave so quickly after having been reappointed."

Mr Cooke was widely considered a good candidate to become president of the Court of First Instance last year. The role was subsequently taken up by the Luxembourg judge Marc Jaegar.

He played a prominent role in the Microsoft case during both the cross-examination of the barristers and as rapporteur - when he drafted the court's landmark judgment.

Mr Cooke was also widely considered as one of the top barristers of his generation when he worked in Ireland, particularly in the field of competition law.