The two companies are fantasy sports providers that allow users to create virtual sports teams, the performance of those teams mirrors their real life counterparts with users receiving cash prices if their teams are successful.
DraftKings was formed in the US, with FanDuel hailing from Scotland.
The merger is believed to have been done out of necessity with both sites facing regulatory and legal challenges into potential violation of individual state gaming laws in the US.
It is not yet clear whether both brands will be maintained following the merger.