The firm said its Hospira UK Ltd site at Park Royal, north London, was expected to shut by August next year.
Its packaging and distribution site in Havant, Hampshire, is set for closure by the end of 2020.
The plans are part of an ongoing review of Pfizer's worldwide operations and are not related to the outcome of the EU Referendum, the firm said.
Pfizer proposes transferring work currently undertaken at its Havant facility - which employs more than 270 people - to its site in Puurs, Belgium.
The Park Royal site - which has about 100 staff - is due to complete production in May next year, with a site exit in August.  However, the firm said it was subject to consultation.
It added its decision to close the Park Royal site was based on it being "an ageing facility which will require significant investment in the near future and due to the expiration of the building lease".
A Pfizer spokeswoman said the plans were not a reflection on the "excellent work performed by our colleagues" and "in no way related to the result of the Brexit decision".
The firm will work to support affected staff who will be considered for "a limited number of positions elsewhere within Pfizer", she added.
Pfizer plans to sell the Havant site as an ongoing pharmaceutical manufacturing facility.
The firm said it would work to ensure its north London customers, with existing contracts, were able to find a new supplier without any disruption to supply.
Leader of Havant Borough Council Michael Cheshire said the authority had tried to convince Pfizer to remain in the town but added "global economic forces have prevailed".
He said it would now seek to support affected staff.
More than 370 jobs are at risk after the US drugs giant Pfizer announced plans to shut two of its UK sites.