CDW plans to buy Sirius Computer Solutions from private investment firm Clayton, Dubilier & Rice for $2.5bn (£1.8bn).
The proposed all-cash transaction, which is subject to customary closing adjustments, is set to close in December 2021.
At 10:04am EST (UTC-5) CDW shares were up 4% to $185.75 on the Nasdaq.
Sirius has around 3,900 clients
Founded in 1980, San Antonio, Texas-headquartered Sirius provides secure, mission-critical technology-based solutions for approximately 3,900 large and mid-sized customers. Last year it generated sales of $2.04bn.
The combined company would have had 2020 net sales of $20.5bn compared to the $18.5bn in sales CDW reported for its full-year earnings.
"Combining our businesses will accelerate progress on our three-part growth strategy by augmenting our portfolio and enhancing our ability to deliver customer-centric outcomes across the full technology solutions stack and lifecycle," CDW president and chief executive Christine Leahy said in a press release.
Sirius adds $0.62 to EPS
The company said the transaction is expected to immediately increase CDW's gross margin by approximately 110 basis points and add $0.62 to non-GAAP earnings per diluted share.
Lincolnshire, Illinois-based CDW is a provider of IT equipment, software and services.