For close on a decade, Senator O'Toole has been the dominant voice in Irish education. He owes this status to his media savvy, his negotiating skills and the unsurpassed level of access he enjoys in Leinster House and elsewhere.
But his success also owes much to a personality which could be described diplomatically as "larger than life". The story of broadcasters Sean O'Rourke and David Hanly collapsing in laughter after one of his Morning Ireland interviews is now part of media folklore.
Senator O'Toole had been questioned about plans by the then minister for education, Ms Niamh Bhreathnach, to use existing funds to reform early childhood education. Primary education, he said, was like an old car going along with four bald tyres. And now the minister wanted to use the spare wheel for petrol money.
It was a classic Joe O'Toole soundbite of the type that has made him the Republic's best-known figure in the field of education. He came up with another such line recently when this reporter asked him about the differences within the INTO on the new national pay deal, which he championed.
"People won't believe it, but I actually enjoy all the whole debate. I never sleep well at night . . . unless I have had a good argument during the day," he told me.
Senator O'Toole's sense of humour belies his considerable achievements over the past decade. Traditionally, teaching unions concentrated on pay and conditions for members, and not much more. But he has made the INTO a progressive and radical voice on a range of issues from child sex abuse to immigration to educational disadvantage.
His principal achievement has been his ability to lead, as well as to follow, his 25,000, mainly female, members.
The INTO, for example, endorsed the Department of Education's new system of school inspection and other accountability measures that were viewed with suspicion by the other teaching unions. Senator O'Toole has a strong record of achievement in terms of securing better pay and pensions for his members, but he has also sought to upgrade the status and professionalism of teachers and to develop the curriculum. Frequently, it has been the INTO, rather than the Department of Education, which has been driving policy. Under Senator O'Toole, the organisation has placed a strong emphasis on in-service training and professional development. It has also been the leading proponent of the Teaching Council, the new professional organisation for teachers which will be established shortly.
The INTO, rather than the Department of Education, also runs a series of summer in-service training courses for primary teachers. It is said to have produced more policy statements in the past decade than the Department. Senator O'Toole remains hugely popular within the INTO, but he is vulnerable to the charge that he misread the mood of his members over the new national pay deal. He strongly endorsed the Programme for Prosperity and Fairness and expected a powerful show of support from INTO members. In the event, the vote was secured by the narrowest of margins, 50.5 per cent to 49.5 per cent.
Inevitably, there has been some sniping that Senator O'Toole, as a big wheel in the ICTU, has been pursuing a Congress rather than an INTO agenda - a charge he vigorously denies. There has also been criticism of what is seen by some as his presidential style. As one source said: "It would be easier to get an appointment with President Clinton sometimes."
With his negotiating and media skills, Senator Joe O'Toole will be a hard act to follow. But he has few pretensions about his record.
"Anything I have achieved is down to the support of a strong executive over the years. Now, I want the next general secretary to be better than me," he said last week.