I'm a barrister, came from another career but changed younger (late 20s). I know some people who've joined profession late in life. All has exceptional careers first - senior civil servant giving advice to ministers regularly who went into administrative/govt law, consultant surgeon who went into medical law, professor of law who went into public law. I know a nurse who left the profession in her late 20s/early 30s and is now a very well regarded KC in an unrelated area, and a social worker who left that after about ten years and went into children's law. Most however join when they're in early 20s
It would be unusual to transfer in without an extremely successful career before. You're not, realistically, going to be compared to what other applicants (who are say 24) have achieved. You'll be compared to what barristers of your age have achieved, albeit in a different field. So perhaps if you're regularly published, that might be seen as similar to doing lots of high profile cases. If you have taught and trained others that might be pertinent. If you've won prestigious funding or awards that might be getting towards an equivalent of being a KC (50 is about the age where most people wanting to become a KC would be applying/appointed, perhaps a bit younger).
Also, perhaps it doesn't look onerous on paper, but you'd have to do a law degree (or at least a conversion course, 1 yr) then the Bar course (1 yr). You'd want to get the highest grades in both to increase chance of pupillage.
Then you'd need pupillage. This is where the bottleneck hits, there are way more applicants than spaces. For example we take 2 a year and we got about 400 applications this year iirc. Then you do that for a year and if you pass, you become a barrister. You also have to get tenancy, either at the chambers where you did your pupillage, or if they don't vote to keep you on, find another chambers and do another 6 months before a further vote!