Lloyd-Williams will oversee the leadership team and focus on "delivering outstanding, innovative and profitable communication plans".
He joined Vizeum in 2014 after spending six years at MediaCom, where he rose from digital strategist to strategy director. He also worked at MediaCom Beyond Advertising during that period.
Lloyd-Williams will report to Tracy De Groose, chief executive of Dentsu Aegis Network UK and Ireland.
Morris will become chief growth officer EMEA at Dentsu Aegis Network, reporting to Nigel Morris, chief executive of Americas and EMEA.
Morris has been at Dentsu Aegis for 22 years. Before joining Vizeum in 2012, he worked at Carat.
De Groose said: "Vizeum has always had a reputation for innovative and creative media thinking, something that Richard Morris has been pivotal in cultivating.
"In Jem, the agency has someone that embodies these qualities, and combines them with strong background in both content and digital. This will ensure that the business and its clients make the most of the opportunities that the current media landscape presents. "
Some of Vizeum’s biggest clients, including Ikea and 21st Century Fox, are currently reviewing their media agency requirements.