It's the Canadian chain's latest attempt to fend off growing competition from other coffee retailers.
Tim Hortons faces stiff competition in the market it used to dominate, with rivals like Starbucks and McDonald's luring customers away with darker, stronger brews.
The new dark roast will be offered at select locations in Columbus, Ohio, starting Monday and London, Ont., starting Nov. 4, Tim Hortons announced Monday.
The dark roast will be offered alongside the store's original premium blend.
London has served as the company's Canadian test market for many new products, including the popular iced cappuccino launched in 1999.