O'Neill will step away at the end of July to be replaced by Geoffrey Yu, who transferred from the UBS investment bank to the wealth management arm earlier this year.
Yu will maintain his role as an ultra-high net worth investment strategist and will work alongside deputy head Caroline Simmons and cross-asset specialist Dean Turner.
O’Neill joined UBS from Merrill Lynch, where he was chief investment officer of wealth management for EMEA, in February 2013. He has also worked at HSBC Investments, JPMorgan Chase and Barclays Wealth.
"Bill has been an enormous asset to UBS Wealth Management in his time here; his insights have been invaluable and he will be greatly missed," said a spokesperson.