The First Minister warned that the Scottish Government has been "left in the dark with both hands tied behind our backs" in attempting to offset the worst impact of leaving the EU.
Key sectors like the NHS are already feeling the brunt of the looming EU departure and her Government won't be able to offset the worst of it, the SNP leader said as she appeared before a meeting of Holyrood committee convenors today.
She added: "Instead of the UK Government opening up negotiating space that increases the possibility of reaching a deal that can attract political support, they seem to be closing down that negotiating space and digging themselves deeper into the hole that they're got themselves in.
"I am increasingly concerned, literally with every day that passes, now that the prospect of a no deal is becoming ever greater.
"As things stand just now I think no deal may actually be the most likely outcome and that is deeply concerning.
"And given that we are two and a half years on from the vote, five months away from exit it is staggering incompetence that a Government has allowed the situation to get to this stage.
"Brexit is frankly shaping up to be the biggest failure of Government policy and handling of a situation that any of us have seen perhaps in our entire lifetimes."
Ms Sturgeon told MSPs that the Scottish Government is doing a "considerable amount" of contingency planning to help mitigate the worst impact of Brexit.
"It's not easy - we're doing that largely in the dark at the moment because we don't know - any of us - the way in which the UK will leave the EU or the basis in which it will do so.
"We're working with a range of different stakeholders and partners, the business community, other organisations and local authorities."
The Scottish Government has been working with local council body Cosla, with a joint "officials group" having been set up to look at operational preparedness.
"That group is meeting monthly," the First Minister siad.
"We've also seconded a member of Scottish Government staff to Cosla to help them co-ordinate their Brexit preparedness."
Brexit Secretary Mike Russell has also met with Cosla President Alison Evison and will do so again later in the Summer, the First Minister added.
"We are doing all of this work really in the dark with our hands tied behind our backs. We don't yet know five months before the due date for exit what the basis of the future relationship will be or even what some of the withdrawal issues are - or whether there will be at all, whether we will be in a no deal scenario."
But she warned: "We're not going to be able to take away all of the impact of Brexit, particularly if we find ourselves in a no deal scenario."
The First Minister warned that the agricultural and hospitality sector are likely to be hit "particularly hard" by staffing shortfalls after Brexit and work is being undertaken to help alleviate the worst of this, while the NHS, social care and universities are also likely to suffer.
"Some of the those areas are already starting to feel the brunt and some of the anecdotal evidence suggests that that is beginning to hit."