Stan Blackley, who was forced out as Yes Scotland's deputy communities chief, also claims the group has become "little more than an SNP front".
He says his former employer is now staffed by "survivors", SNP secondees and "random stooges".
The campaign group, led by ex-BBC journalist Blair Jenkins, was launched in 2012 to lead an eclectic independence movement, including non-nationalists.
Blackley, a former chief executive of Friends of the Earth Scotland, was brought in to help organise a bottom-up grass-roots campaign.
However, Yes Scotland was widely believed to have overspent on directors, and ended up shedding senior staff. Blackley left in January after over a year in the job.
In an exclusive article for today's Sunday Herald, he describes the wider Yes movement - hundreds of local groups and ambassadors - as a runaway success, but claims Yes Scotland is "redundant".
He says the body was "ill-devised and dysfunctional from the start and continues to underwhelm due to a lack leadership, strategy and resource."
At Yes Scotland he says he saw "more roaring tantrums, faux resignations and bad-tempered walk-outs" and "more pointless meetings, badly-planned, chaotic activities and last-minute panics" than in the rest of his 25 working years.
Problems at Yes Scotland, he writes, resulted in the SNP taking it over. He says the group has recently become "little more than an SNP front", with the SNP's vision of independence the only one articulated, which he found "depressing and counter-productive".
Blackley also says the Scottish Greens, a key component of the cross-party movement, had "quietly created distance between itself and this SNP-led Yes Scotland". On the polls moving slightly away from the No campaign, Blackley claims this is "in spite of Yes Scotland, not because of it".
A spokesman for the pro-UK Better Together said: "This confirms what everyone already knew. There is no Yes Scotland, there is only the SNP. It makes a joke of Alex Salmond's claim that a vote to break up the UK is not a vote for him."
A spokesman for Yes Scotland said Blackley was dismissed in a "change of initiative in the grass-roots area". He added: "We are grateful to Stan Blackley for the contribution he made."