President McAleese's term of office runs until November of next year and Mr Finlay has conceded that it is early to be declaring for the campaign.
Mr Finlay recently topped a presidential poll of some 10,000 callers to Joe Duffy's show. He said afterwards: "I'm not often speechless, but something like that forces you to think, doesn't it?"
In his letter to the Labour Party he says, he hopes his early declaration with kick-start a "vigorous" debate in the party about the issue.
"In seeking our party's nomination now, what I am asking for is not an immediate decision, but a dialogue within Labour about the values that should inform our entire approach."
He adds that dialogue was needed about "the message we should take to the people, the mandate we should seek, and how we should set about winning this crucial election with a professional and committed campaign".
Mr Finlay said he was motivated by "an incredible sense of betrayal" he experienced in the course of his work with the children's charity.
The Church and banks scandals, together with the failures of political institutions, had "undermined respect for any form of authority".
He wanted to "attempt to reconnect" and "try to offer some kind of alternative vision as to where we can go".
Asked about the possibility of running against former Taoiseach Bertie Ahern he replied: "I'm looking forward to it already."
Mr Finlay was senior adviser to former Labour leader Dick Spring in three governments and centrally involved in the election of President Mary Robinson in 1990.
His letter was sent to the party leader and to all the Labour TDs, senators and national executive members.
A spokesman for Mr Gilmore said that while the move came as no surprise, it would be next year before Labour decided on the issue.