The pan-European STOXX 600 index ticked up 0.2% reversing early gains. Spanish shares rose 0.8% to lead gains among regional peers as Inditex shares scaled a two-year high after posting a strong profit growth.
JD Sports' 9.5% drop was the biggest on the pan-region index. The sportswear retailer posted its worst day in 3-1/2 years after its largest shareholder, Pentland, sold a part of its stake.
That cancelled gains on London's benchmark FTSE 100 index which closed flat. An index with more domestically focused British firms slid 0.6%.
Britons vote on Thursday in an election that should decide the fate of Brexit. Polls now predict only a modest majority for Prime Minister Boris Johnson, an outcome that could prolong uncertainty and further hit investor sentiment.
The benchmark European index scaled four-year peaks in the past two months on optimism around an eventual departure for Britain from the European Union as well as hopes of a resolution to the U.S.-China trade war, but sentiment has lately been dampened by conflicting headlines on both.
A Sino-U.S. trade deal remains elusive ahead of the next round of U.S. tariffs on Chinese imports due on Dec. 15, but latest reports suggest that tariffs could be postponed.
A policy decision by the U.S. Federal Reserve later in the day is also in focus. The Fed is widely expected to keep borrowing costs steady, signalling the start of policy stability. On Thursday, newly appointed ECB chief Christine Lagarde is expected to strike a similar tone.
"Equity markets should be in for a couple of days where they see the confirmation of what they priced and therefore there should a modest lift that comes from that," said David Page, senior economist at AXA Investment Managers in London.
But if any one of the events delivers a surprise, it could lead to a more negative outlook, he said.
Among other shares, German engineering company Siemens was among the biggest boosts to the STOXX 600 after it named its strategy chief and former Kuka CEO Horst J. Kayser as boss of its loss-making portfolio companies.
By Susan Mathew and Medha Singh