Under a "major three-part transaction" with Novartis, GSK will own also 63.5% of a newly-created consumer healthcare business.
GSK said it would use proceeds from the deals to return £4 billion ($6.7 billion, 4.9 billion euros) to its shareholders.
In a separate statement, US pharmaceutical giant Eli Lilly said it had reached an agreement to acquire the Novartis animal health division for $5.4 billion.
GSK chief executive Andrew Witty said his company's agreements with Novartis -- expected to be completed during the first half of 2015 -- accelerates the British firm's "strategy to generate sustainable, broadly sourced sales growth and improve long-term earnings".
He added in the statement: "Opportunities to build greater scale and combine high quality assets in vaccines and consumer healthcare are scarce.
"With this transaction we will substantially strengthen two of our core businesses and create significant new options to increase value for shareholders."