Places affected include restaurants, pubs, shops, cinemas, shopping centres, leisure centres, enclosed workplaces, public transport.
He added: "My worry would be if we did not have the universal ban, then we would not have a level playing field between establishments."
The launch was at the Java Bean café in Glynneath, which has been non-smoking since it opened three and a half years ago.
Joint café manager Pauline Morgan said: "It's something we feel is important, it's our little bit towards improving the well-being of our community."
Helen Dallow, landlady of the Belle Vue pub in Merthyr Tydfil, said she accepted the ban and plans to create a smokers' garden.
She said her biggest concern was policing it.
"Some customers won't take kindly to being told they won't be able to smoke, and that I think is a major worry." she said.
Kieron Walker, from Merthyr Tydfil, a smoker for over 30 years, said he was against the ban "totally, 100%".
"Everybody's got the right to smoke if they want to, " he said.
'Stub it out'
But Leanne Jones, who has smoked for eight years, supports the ban, saying it may get her motivated to quit.
"It will be hard, but it is something you're just going to have to get used to," she said.
Smoking-related illnesses like heart disease and lung cancer are among Wales's biggest killers, causing 6,000 premature deaths each year.
Chief medical officer, Dr Tony Jewell, said: "The damaging health effects of second-hand smoke in enclosed public places cannot be underestimated and the time has come to stub it out once and for all."
Singers Bryn Terfel and Shirley Bassey, cyclist Nicole Cooke and Welsh TV presenter Gabby Logan have posted messages of support on the smoking ban website.