Basel-based Novartis had previously acquired the rights to Ofatumumab for oncology indications, but it is currently being developed for relapsing remitting multiple sclerosis and other auto-immune conditions.
"Novartis is pleased to further reinforce our commitment to neuroscience and to add an exciting new treatment to our strong MS portfolio," David Epstein, head of Novartis Pharmaceuticals, said in a statement.
Novartis will pay GSK $300 million up front to buy the compound and a further $200 million is payable after the start of a phase III study in MS by Novartis.
Payments of up to $534 million will be made if pre-agreed milestones are met.
Novartis will also pay royalties of up to 12 percent to GSK on any future net sales of Ofatumumab in auto-immune conditions.