In Motion makes rugged and secure mobile routers for vehicles.
It generated US$15 million of revenue in 2013, with a gross margin of 50 per cent of revenue.
Sierra, which makes a range of communications equipment, says the businesses are complementary and the deal will broaden and strengthen its portfolio.
Sierra says it is aiming for between US$112 and US$116 million of revenue for its fourth quarter, according to guidance released in November.
The deal, which requires court approval, is expected to close in early March.