The search engine took a 38.1pc market share across the continent in December, surpassing Internet Explorer's 37.5pc - the first time Microsoft has lost the top spot in a leading market.
Google Chrome saw its share rise to 14.6pc from just 5.1pc a year earlier.
Aodhan Cullen, chief executive at web analytics specialist StatCounter, which compiled the data, said: "This is the first time that Internet Explorer has been dethroned in a major territory. This appears to be happening because Google's Chrome is stealing share from Internet Explorer while Firefox is mainly maintaining its existing share.
"We are probably seeing the impact of the agreement between European Commission competition authorities and Microsoft, to offer EU users a choice and menu of browsers from March last year," he added.
Since early 2010, Microsoft has offered millions of European customers that use its Windows software the option of using 12 different internet browsers.
This followed an agreement in December 2009, when European Union regulators accepted Microsoft's pledge to give consumers better access to rival browsers, ending a long antit-rust dispute.
Despite the European setback, Internet Explorer retained a clear lead in the browser market in North America with a 48.92pc share - followed by Firefox at 26.7pc, Chrome at 12.82pc and Safari, 10.16pc.