Patients and visitors will be banned from smoking anywhere at Guy's Hospital and St Thomas' Hospitals from Friday 19 June, the NHS foundation trust has announced.
As well as the two main hospital campuses, the ban also applies to community health facilities run by Guy's and St Thomas' NHS Foundation Trust.
"We want patients, staff and people visiting our hospitals or community sites to know that we care about their health and that we are doing everything we can to make Guy's and St Thomas' a healthy environment for everyone," said chief executive Ron Kerr.
"While we know that giving up smoking can be a real challenge, there is overwhelming evidence that doing so will help our patients' chances of successful treatment and a swifter recovery.
"People who get NHS support to stop smoking are four times more likely to give up smoking for good. So we will be encouraging anyone who uses our services or lives locally to use the NHS stop smoking service to get the help they need to kick the smoking habit."
Mike Salmon, 57, from Rotherhithe, gave up a 20-a-day smoking habit in June 2014. He said: "I started smoking when I was 20. In those days lots of people smoked, even at work. I tried to give up smoking a couple of times but I just couldn't quit.
"In September 2013, I had a pain in my chest and went to A&E where I had an X-ray and was found to have pulled a muscle. My GP saw the results and was concerned about my lungs so referred me to the chest clinic at St Thomas' Hospital.
"Thankfully the consultant ruled out cancer but he said I had bronchial problems which would affect my breathing if I didn't stop smoking.
"I haven't smoked a cigarette since. What's different this time is the support of the stop smoking service. They have kept me focused on what I'm trying to do."
Staff at the two hospitals were banned from smoking in January last year.
Smoking inside the hospital buildings at Guy's and St Thomas' has been banned since 2005.
• For more information about Guy's and St Thomas' stop smoking service and how to get help call 020 7188 0995 or email: email@example.com