Leading older people's charities Help the Aged and Age Concern England will be merging in April next year.
Trustees of each charity made the decision after receiving positive reports on the merger proposal and they are now looking to appoint a chief executive of the new, as yet unnamed organisation.
Dianne Jeffrey, current chair of the Anchor Trust, has been named as chair of the new charity and will take up the new role on 1 October.
Ms Jeffrey said: "We are now at a very exciting, advanced stage in the process of creating a new organisation which will work with and for older people. Progress has been steady and real milestones reached.
"The process of recruiting a new chief executive is already well advanced and we can now move to finalise the recruitment of someone to lead the new organisation into the future."
The charities will now draw up a legal transfer agreement and appoint a new board of trustees.
Catherine McLoughlin, chair of Age Concern England said: "This has been a long process with a large number of complex decisions, but we are now approaching the end game. Barring unforeseen, insurmountable differences, we expect the new charity to begin operating in Spring 2009.
"This is a hugely exciting time for everyone involved in both charities - and indeed for the voluntary sector as a whole. We can boast with some legitimacy that the new organisation will be one of the most powerful, campaigning voices in the UK.
"Our respective staff, volunteers, partners, donors and beneficiaries can be assured that the new charity will get to work straight away on the growing agenda connected with age and ageing."
Jo Connell, chairman of Help the Aged said: "No one should underestimate the task ahead nor the sheer hard work that has got us to where we are now.
"Older people, here in the UK and internationally, deserve the best and we believe the new charity will be precisely that. Our aim is to place age and ageing at the centre of public debate.
"It is our intention to build on the strengths that exist within Age Concern England and Help the Aged and improve them even further - enhancing the fantastic work that both charities have completed over the years.
"We believe the new charity will provide even better services and support for older people, be able to raise even more funds, have greater influence and be able to exert more pressure on policy makers."