"This is excellent news... and a further boost following the England team's recent achievement in becoming the world's number one ranked test side," England and Wales Cricket Board chief executive David Collier said in a statement.
"The extent of their investment reflects the fact our five-day game continues to command very significant audiences, both at home where we achieved record attendances for international cricket in 2011 and abroad."
The sponsorship agreement will begin next year when England host test series against West Indies and South Africa.
Investec becomes only the third firm to sponsor test cricket in England, succeeding Npower and Cornhill.
The company recently ended its 12-year backing of England's November rugby internationals.
