Dolan had only been a member of the group for a few months before the split, reported Digital Spy.
The band released a statement saying: "We part ways with fond farewells.
"Emily played a huge part in the recording of our new album Last Of Our Kind and makes a final appearance in the video for our single 'Open Fire', which is coming to a screen near you soon. Good luck, Emily!"
Dolan had previously been a session musician, working with the likes of Bryan Ferry and Tricky.
She made her live debut with The Darkness on March 6.