Amanda McLean, chief executive of the Institute of Fundraising, has resigned with immediate effect after only four months in the job.
McLean, who took up the post in November last year, said she decided to leave so that she could spend more time with her family.
"I have done full-time jobs before and I knew this would be hard work, but some jobs have greater flexibility than others," she told Third Sector. "The job was too overwhelming. There is so much happening in the sector.
"It is an amazing job, but the hours weren’t working out for me. I have children at primary school and I was only seeing them for a couple of hours in the evenings and at weekends."
McLean said she missed having a direct link with a specific charitable cause.
Asked why her decision to resign was with immediate effect, she said: "I’m still doing the new chief executive work, meeting people and telling them what my vision is for the institute, and people don’t take you seriously doing that if they know you’re leaving."
She said she had told Alan Gosschalk, acting chair of the institute, that she wanted to leave. "He felt it would be less unsettling for me to step down with immediate effect," she said.
McLean said she had not been asked to step down. "I wasn’t pushed at all and I really don’t want people to think that,"she said. "It is all amicable and friendly."
She said she decided to step down only "two or three days ago" and she did not yet know what she would do next.
A statement from the institute said: "It is with regret that the institute is announcing the resignation of chief executive Amanda McLean with immediate effect."
It said Bruce Leeke, chief operating officer at the institute, would take over as interim chief executive while the board considered the recruitment process for a permanent successor.
Alan Gosschalk, acting chair of the institute, said: "I would like to take this opportunity to thank Amanda for her contribution to the work of the institute over the past few months and to wish her all the very best for the future."