North Lanarkshire Council, responsible for 160 schools, approved the decision at yesterday's meeting.
The authority said it had a "moral duty" to impose the ban given major problems with childhood obesity across Scotland.
Council officials will now look at implementing the policy, with the council agreeing an exclusion zone of 250 metres from schools.
North Lanarkshire said it had already agreed to increase investment in its breakfast clubs by extending the service to all schools where 20% or more pupils qualify for free school meals. Earlier this month the Scottish Government and Cosla published Better Eating, Better Learning - an in-depth report setting out a new context for school food.
East Ayrshire Council made a similar move last year, while Glasgow introduced a 300-metre ban with limited success in 2009.
Cllr Jim Logue, convener of North Lanarkshire's learning and leisure committee, who proposed the move, said: "We have a moral duty to do everything we can to look after children's health.
"We accept that this is not a complete solution to the problem of obesity but we can't sit on our hands here."
East Ayrshire's 250-metre carries the threat to a burger or ice cream van's street trader's licence, effectively putting it out of business, and the potential for a fine.
But a recent report on Glasgow's ban warned that mobile vans continue to operate close to schools.
Glasgow also carried out a survey of the food pupils at five schools were eating when they went outside the school gates at lunch-time.
Three of the schools were surrounded by a heavy concentration of outlets including chip shops, kebab shops, bakeries, sandwich shops and supermarkets. There were more than 30 outlets within 10 minutes walk of one school.
Glasgow said that many European countries had achieved successful healthy school food policies "without recourse to such detailed legislation".