The new 14-story building will house leading-edge cancer specialists from around the world, including 70 from King's College London.
The £160 million cancer centre aims to place itself alongside the world-renown reputations of The Royal Marsden and The Christie in Manchester, as leading the way in cancer treatments.
Dr Majid Kazmi, clinical director of cancer services at Guy's and St Thomas' NHS Trust, told the Evening Standard newspaper, “This has been a 10-year project to make Guy's a global centre of excellence for cancer medicine.
“We are already attracting some of the best brains nationally and internationally to come and work here.
“When we did an analysis, we realised that about a third of all the activity going through Guy's and St Thomas' was cancer-related. We thought, 'We have got to get good at this!'"
The centre begins a period of phased opening and prides itself on improving the patient experience, from its design, to location of treatment areas.
“Today is the culmination of more than 10 years of planning and working in partnership with our patients to create a building to transform cancer care," said Dr Kazmi.
Along with well-researched design and layout the centre is also the first in Europe to have its radiotherapy treatment rooms above ground level, in response to patient feedback about how to improve the patient pathway.