TransferWise, the money transfer company that's taking on Western Union, is valued at $3.5 billion after a new investment round, making it Europe's most valuable financial technology start-up.

In lowering fees and adding a slick online platform to help consumers move money globally and track their transfers, the London-based company is taking a modern approach to a staid business that's been dominated by giants like Western Union and MoneyGram.

The company says it's been pushing for more transparency around the fees banks and currency exchange services charge their customers for transferring money abroad.

"Eight years ago we had a dream, and in a way the whole world was against us," said TransferWise co-founder and Chairman Taavet Hinrikus in an interview. "And we've been able to step by step build the business and also change the environment around us to be much more consumer friendly."

TransferWise isn't adding fresh cash to its balance sheet with the investment, but is instead giving employees and early investors the chance to sell some of their stake in a $292 million secondary deal.