The content will be displayed alongside existing Holiday.co.uk products in the flights, accommodation, cruise and cottages sectors.
The development is a coup for Belfast-based Activitybreaks.com as it will thrust its array of holidays into another market.
Activitybreaks commercial director Katy Knox said: “As Activitybreaks.com offers considerable commission on all bookings referred from our affiliate partners, there is a real opportunity to create additional revenue from their site.
“Also, because Activitybreaks.com specialises in over 2000 breaks that are not available from traditional tour operators, this can be a chance to offer the customers something really different.”
Dave Dibble, e-commerce director at Holiday.co.uk, added: “We wanted to link with a strong brand like Activitybreaks.com that already had an established presence in the market.
“With Activitybreaks on board we can now effectively address the very important question which many of our customers ask – what can I do when I get there?”