Jackie Ballard, chief executive of Womankind Worldwide, has announced her resignation just 10 months into the role.
Womankind Worldwide is an international women’s rights charity that works with local organisations in Africa, Asia and Latin America.
Ballard, who joined from the top job at Action on Hearing Loss in September 2012, said she would leave her post in mid-August because she missed direct contact with beneficiaries.
"I didn’t realise until I was well into the job that what motivates me in my work is direct contact with the beneficiaries of a charity," she said.
"At Womankind, the beneficiaries are overseas and we work with partners who in turn work with the beneficiaries. Nobody misled me about the job, but you can’t fake it as a chief executive and, when I realised what motivates me, I had to go.
"I have not given much thought to what my next job will be, but I think I would like to stay in the charity sector, either as a chief executive or an interim chief executive."
Ballard had been at Action on Hearing Loss for five years and led the RSPCA as its director general for a similar period of time before that.
She was the Liberal Democrat MP for Taunton between 1997 and 2001.
Ballard said she had already helped Womankind Worldwide to implement a new strategic direction during her short tenure, which she hoped would lead to it becoming the "go-to" organisation for international women’s rights.
The charity said it had begun the process of recruiting a new chief executive.
"We are immensely grateful to Jackie for all that she has done for Womankind in her time with us, and we are very sorry to see her go," said a statement from Julie Ashdown, chair of Womankind Worldwide. "She has brought great clarity to the development of our new strategy and her wisdom and experience have ensured that she will leave a lasting legacy at Womankind."