The Nets and Porter reached an agreement Wednesday on an offer sheet that would pay Porter the maximum of $106 million over four years.
The Wizards had two days to match the Nets' offer. They had made it clear they intended to exercise their right to match any offer to Porter, a source reiterated to ESPN's Ohm Youngmisuk on Tuesday night.
Porter now becomes the highest-paid Wizards player and has a no-trade clause for the season.
The Wizards' salary increases to $126.5 million with the match of the offer sheet, and their current tax bill is $11.4 million, with 13 guaranteed and two non-guaranteed contracts.
The Nets' cap space will not be available until Porter reports and passes a physical in Washington. Brooklyn will have $28.3 million in cap room once the deal is completed.
The third overall pick by Washington in 2013, Porter finished fourth in the voting for Most Improved Player last season after posting career-high averages of 13.4 points, 6.4 rebounds and 1.5 steals while shooting 51.6 percent from the field and 43.4 percent from 3-point range.
Porter became a serious 3-point threat, increasing his shooting from beyond the arc from 36.7 percent from the season before. He started 80 games and became a third scoring threat to complement John Wall and Bradley Beal.
Information from ESPN's Bobby Marks was used in this report.