The FTSE 250 group said it has signed heads of terms to acquire a portfolio of "selected UK health facilities management contracts" from Carillion, for a total consideration of £50.1m. The operations are expected to be fully integrated by the end of 2018.
The contracts provide facilities management support services to over 50 NHS sites across the UK, including five acute hospital trusts, Serco said. The portfolio of contracts is profitable and has current annual revenue of approximately £90m and a weighted average remaining term of 14 years.
Meanwhile, the company has also shelled out $20m (£15m) for BTP, with the deal set to complete "around the end of next year".
Serco said BTP's "deep capabilities within the satellite and radar industries, where it provides maintenance, repair and overhaul, testing facilities, and related systems and field engineering services" complement the group's existing ship and shore modernisation work.
"BTP operates in a growing segment of the market and through its combination with Serco we will be able to target additional revenue and cost synergies," said Serco chief executive Rupert Soames.
"We welcome our new colleagues joining Serco and look forward to working together as we further develop our scope, scale and excellent reputation in the US defence sector."
Last week, Serco announced the departure of its chief operating officer, Ed Casey, who is stepping down after four years of making a transatlantic commute.