The law in England encompasses offices, factories, shops, pubs, bars, restaurants, membership clubs, public transport and work vehicles that are used by more than one person.
The ban will also mean that indoor smoking rooms for employees will not be permitted.
Patricia Hewitt said: ‘This is a triumph for public health and a huge step forward for health protection. Thousands of people's lives will be saved and the health of thousands more protected. Smokefree legislation will protect everyone from the harm of secondhand smoke when working, socialising and relaxing and will provide a more supportive environment for smokers who wish to give up.
"The scientific and medical evidence is clear - secondhand smoke kills, causing a range of serious medical conditions including lung cancer, heart disease, and sudden infant death syndrome "SIDS" in children. This legislation will help to prevent the unnecessary deaths caused every year from secondhand smoke, and recognises that there is absolutely no safe level of exposure’
The Health Secretary also launched a new Smokefree England campaign which will help the country's 3.7 million businesses including nearly 200,000 pubs, bars, restaurants and other leisure outlets prepare for the implementation of the legislation.