Siggi Bennett, a member of the Scottish bar since 1982 and author of several legal textbooks, described the Faculty of Advocates as reactionary and undemocratic in the face of a crisis engulfing the profession.
Mr Bennett claimed the Edinburgh-based organisation "excludes accountability at every level" and has failed to protect its members' interests against the threat from solicitor-advocates.
He said solicitor-advocates have been taking over an increasing share of the legal workload since they were first allowed to appear at the High Court and Court of Session in 1990.
Previously, solicitors had to instruct an advocate to act on their behalf for clients when cases reached Scotland's highest courts.
Advocates are also said to be increasingly concerned about the future of the profession in the face of Lord Gill's proposed court reforms.
They would bar cases worth less than £150,000 from the Court of Session. The current threshold is £5000. A source close to the Faculty said it could spell "the beginning of the end" for the profession as available work is slashed.
The warnings come ahead of the inaugural lecture to the faculty by new Dean, James Wolffe, QC, on May 7.
Mr Bennett said: "Democratic bodies everywhere accept responsibility to engage their electors' interest, to go out of their way to inform them as to the issues of the day, but this is quite alien to the culture of the Faculty of Advocates.
"Here it is acceptable that our representative body, the Faculty Council, should to all intents and purposes be invisible, not properly accountable, its electorate remote, disengaged and apathetic."
Mr Bennett resigned from the Faculty council in 1996 after junior members were forbidden to question office-bearers, and he says the routine circulation of agendas and minutes from meetings was halted "without notice or explanation".
Mr Bennett is at odds with the faculty over his support for scrapping the need for corroboration in criminal cases, and the not-proven verdict, and wants television cameras in Scots courtrooms.
He said the body was "backward looking" and had failed to react to the competitive threat from solicitor-advocates.
"When we lost our monopoly in 1990, the then Dean of the Faculty Alan Johnstone expressed a complete lack of concern about the advent of competition," said Mr Bennett. "He professed himself totally satisfied that the faculty would hold its own, wouldn't lose any competitive ground.
"And that's the mood of complacency that has pervaded the faculty ever since."
Advocate firms have had to sell off assets and make staff redundant as their case-loads have fallen. The problem is expected to be exacerbated by the Gill reforms. Frustration with the Faculty is said to be widespread among advocates.
A source said: "You can see that there is obviously likely to be a big reduction in work in the Court of Session. But when you have a leadership that is slow to adapt and not business-minded it doesn't fill members with confidence."
Mr Wolffe said: "I have no doubt that many advocates are deeply concerned about the potential effect of the current proposals to reform the courts in Scotland not only on their future livelihoods but also for access to justice. Advocates are not alone."
He added that he is determined ministers should recognise the importance of an independent bar.