Under the terms of the deal, Polycom stockholders will get $3.12 in cash and 1.31 Mitel shares for each share of Polycom common stock, or $13.68 based on the closing price of a Mitel common share on April 13. Mitel's stock closed that day at $8.06 and has fallen 10 percent since then.
The deal is expected to close in the third quarter of this year.
"Together, Polycom and Mitel expect to drive meaningful value for our shareholders, customers, partners and employees around the world," Peter Leav, Polycom's president and chief executive officer, said in a statement.
Polycom's stock fell 2.04 percent Friday, but has gained more than 13 percent in the last three months.
"Polycom is one of the most respected brands in the world and is synonymous with the high quality and innovative conference and video capabilities that are now the norm of everyday collaboration," Rich McBee, Mitel's CEO, said in the same statement.
Mitel shares are down more than 6 percent year to date, but are up 10 percent in the last three months.
— Reuters contributed to this report.