Roberts joins from MyTravel Group, and will report to Alicja Lesniak, chief financial officer at Aegis.
Before joining MyTravel, Roberts held roles as group treasurer at NTL; treasurer at Cable & Wireless Communications; and has held treasury roles at WPP and Sedgwick Group.
Lesniak said: "His appointment reflects an increasing focus on our capital structure, working capital management, and structuring acquisition financing.
"Corporate finance plays a very important part in a company like ours -- both from a financing and an operational perspective."
Aegis has been on the acquisition trail this year, with recent acquisitions including: ad-serving business Bluestreak.com, bought for £6m; event agency Vivid Marketing for £2m; and mobile company Marvellous Ideas for £800,000.