The Cardinals selected the big-hitting strong safety out of Washington State with the 27th overall selection in last month's draft after Arizona traded down from the No. 20 spot, getting New Orleans' first-round pick and a third-round selection.
The contract is worth $7.7 million, including a $3.9 million signing bonus to be paid in increments of $981,000 over each of the four years. A total of $6.9 million is guaranteed because he gets the first three years' salary under NFL rules. The contract includes a fifth year team option.
Bucannon is the highest drafted player from Washington State since Seattle took cornerback Marcus Trufant at No. 11 in 2003.
The Cardinals have now signed all seven of their drafted players.