The firm cited customer demand as the main driver for the investment, explaining that the plan was to add 21,000 square feet of production space, two fill/finish suites and clean rooms.
The expansion – which Merck said will increase current capacity by 90% - is due to be completed this year will support clinical and commercial production.
Merck said the expanded facility will work with both its cell-banking operations in Rockville, Maryland and its viral and gene therapy production capacity in Glasgow, Scotland.
The Carlsbad facility became part of Merck's manufacturing network through the acquisition of Sigma-Aldrich in 2014.
News of the expansion follows just days after Merck announced it had upped bioreactor capacity at its facility in Martillac, France in a move designed to broaden its biologics manufacturing offering.