The group has secured the top five places in a league table of the candidates by the number of votes cast for them.
This means that Derek Salter, George Oldham, Nicholas Tweddell, Colin Brock and Mark Benzie have all secured places on the board.
It gives a dramatic mandate to those, led previously by Ian Salisbury, who have long campaigned to drastically cut back the board's activities.
Thomas Woolley and Sarah Lupton were the only ones not affiliated to the reformers to win seats.
The reform group - which secured the support of Norman Foster, Richard Rogers and Edward Cullinan - had campaigned to win all seven seats on the board that are reserved for practising architects.
However, the result will come as a major blow for those who have backed the board's current stance on such issues as PI insurance, education and continuing professional development.
Those strongly backing the extension into these areas include chairman Humphrey Lloyd, who has made many enemies during his tenure as board boss.
He and chief executive Robin Vaughan have lost a host of allies in the election, including long-term supporters Elspeth Clements and Yasmin Sharriff, who picked up just 140 votes.
Nick Tweddell, one of the chief organisers of the reform group, said he was delighted by the result.
'It was as good as we could have hoped for given the electoral system as it stands - we are very pleased.
'Five seats going to the reform group is great, it means we can really get on with trying to bring about change,' he added.
The turnout of the election was 23 per cent, which compares favourably to many British local elections.