The ban, which will affect a number of motorists, has been brought in to protect under 18-year-olds from second-hand smoke.
Research has shown that one-in-ten kids in Wales are exposed to cigarette smoke in cars and a new campaign is being launched ahead of next month.
Talking to the BBC, Health Minister Mark Drakeford explained the reasoning behind the ban:
"Children are particularly at risk from second-hand smoke, which has been linked to a range of health issues, from sudden infant death syndrome, lung and ear infections and asthma. This danger is heightened when they are in the confined space of a car and can't escape the fumes."
While many motorists will argue that they only smoke with an open window, the health minister has said that “there is evidence that even with windows open, the level of toxic chemicals remains high."
"Together with the forthcoming regulations on standardised packaging these regulations will help to denormalise smoking and discourage children from taking up the deadly habit," said Jamie Matthews of Action on Smoking and Health Wales.
Anyone caught breaking the law will be ordered to pay a £50 on-the-spot fine.
