Hazlitt was recently tipped for a promotion to chief executive of Virgin Radio's parent company Scottish Media Group.
However SMG suspended the recruitment process in December after deciding to commence discussions with Ulster Television about a merger of the two companies.
Hazlitt joined Virgin Radio in August 2005 from Yahoo! UK and Ireland where she was managing director.
She said: "I've had a fantastic time at Virgin Radio and I feel privileged to have been able to work with such a talented group of people, but I have other things in my life that I want to achieve and it's time for me to move on. I wish Paul and the whole team all the success that they deserve."
She is not believed to have lined up another job and is contracted to the station for four months following her departure.
Jackson has been the station's programme director since 2001 and handled the chief executive role on an acting basis for several months during 2005.
Donald Emslie, SMG's acting chief executive, said: "I'm sorry to see Fru go. She's been an inspirational leader for Virgin Radio and her knowledge of the radio and online world has taken the station to the next level.
Emslie said of Jackson that he is "among the best radio professionals in the industry and a great asset for Virgin Radio".
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