Benson will run the administration teams for both the retail and institutional businesses and replaces Maggie Morris who is due to leave at the end of June.
He joins the firm from Aviva, where he was head of PMI claims. He spent 18 years at the company and left during its restructure in September.
Legal & General acquired Cofunds in a deal worth £131m in March and since then there has been a raft of personnel changes.
CEO Martin Davies quit in March, followed by Stephen Mohan, managing director of operational services, in April.
A few weeks ago chairman Charlie Eppinger, viewed as the driving force behind the deal, stepped down.
