Long-serving Aegon UK chief executive (CEO) Adrian Grace will be replaced by Mike Holliday-Williams on 1 October.
Aegon's master trust now manages over £1bn in savers' assets as its overall European life business continues to grow.
Aegon's acquisition of Blackrock's defined contribution (DC) business has "significantly improved" its market position leading to a "strong pipeline for potential contract wins", the provider has said.
Five executive changes have been made at Aegon to reflect its shift from a traditional life company to an intermediated, digital platform business.
Mike Rogers, the former chief executive officer (CEO) of LV=, has been appointed as non-executive chairman of Aegon UK.