The European Court of Human Rights ruled Thursday that France did not violate George Soros' rights when convicting him of insider trading, defeating a years-long effort by the billionaire financier to clear his name.

Though Soros has faced criticism for other investment decisions before and since, the French conviction over trades in 1988 left a particular stain on the Hungarian-born businessman and philanthropist's five-decade career.

He was fined euro2.2 million in 2002, or $2.92 million at current rates, for purchasing shares in French bank Societe Generale in 1988, days after being informed about a planned takeover bid for the bank.

That was the amount he was accused of making when he sold the shares shortly afterward. France's highest court reduced the fine in 2007 to euro940,000 ($1.25 million at current rates).

Soros argued that France's insider trading rules at the time were unclear, and that the length of the investigation — from 1993 until his indictment in 2000 — made it difficult to call reliable witnesses, violating his right to a fair trial under the European Convention on Human Rights.

The human rights court, based in Strasbourg, France, disagreed. In a 4-3 decision, the panel of judges argued that "the law applicable in 1988 was sufficient for Soros to have been aware that his conduct might be unlawful."

The Soros Foundation in Paris would not comment on the decision, and Soros' lawyers could not immediately be reached.