Tillet will take over the £47.4m Allianz UK Growth Fund and the £10.7m Allianz UK Unconstrained Fund, as well as taking on the deputy manager role on the UK Unconstrained Fund.
Thomas was chief investment officer of UK equities for eight years before being moved as the group adjusted its focus to income, mid cap and unconstrained equity strategies.
The bottom quartile performing UK Growth Fund was due to merge with one of its RiskMaster multi-asset funds last year, but the attempt was blocked by investors.