About 120,000 families will have access to the minimum level of financial support, which previously varied among local authorities.
Ministers say the scheme will open ahead of the 2018/19 academic year, with eligibility determined at a local level.
A survey last year found some teachers had personally funded school uniforms for children living in poverty.
The annual costs are expected to reach £12 million, with 50 per cent of the cost met by the Scottish Government and 50 per cent by local authorities.
The clothing grant will be reviewed every two years to make sure the funding remains in line with the cost of living.
Education Secretary John Swinney said: “We know that school uniforms can be a considerable cost for families, which is why we have worked in partnership with Cosla to introduce a new national minimum school clothing grant.
“It will help relieve pressure on families, reduce costs of living and remove the stress and stigma which can often be associated with struggling to afford essential school items.”
Councillor Stephen McCabe, Cosla’s spokesman for children and young people, said: “Every child in Scotland deserves the best chance in life and for too long poverty has blighted the life chances of too many of our children and young people.
“Access to decent clothing is an important part of ensuring children have the best chance of getting the most from their education.
“Therefore it is only right that we do the best we can to create as much of a level playing field as we can in terms of school uniform.”