Cumberbatch's publicist revealed that the couple have parted amicably, reports the Daily Mail.
"They were together such a long time but it just wasn't working anymore," said one insider close to the pair.
The Sherlock actor and Poulet met as students at Manchester University. Poulet has appeared in The Thick of It and its movie version In the Loop.
Cumberbatch, who recently said that he hated his "academic" image, is currently starring in director Danny Boyle's West End production of Frankenstein.