Arena won the business after a competitive pitch against undisclosed agencies. The previous incumbent, Manning Gottlieb OMD, did not repitch for the business. Arena Media will handle planning and buying across both offline and online display activity.
Brightsolid is looking to build awareness of the sites, which it acquired from ITV for £25 million. ITV paid £175 million for the brands in 2005.
The deal brought together Genes Reunited and Brightsolid's family history brands findmypast.com and ScotlandsPeople. The company, launched in 2005 as a subsidiary of the Beano publisher DC Thomson, also has sites overseas such as the Australian portal findmypast.au.
Elastic Creative, the Edinburgh-based agency, handles all the creative work for the Brightsolid brands and is unaffected by the appointment of Arena.
John Robertson, the sales and marketing director at Brightsolid Online Publishing, said: "Arena understood how to reach our target audiences efficiently, with a flexible trading model and a strong set of analytic tools."