When Texans defensive end J.J. Watt signs his six-year, $100 million contract extension that includes $51.876 million guaranteed, he will become the highest-paid defensive player in NFL history.

Watt’s extension surpasses the previous record set by former Texans defensive end Mario Williams, who signed a six-year, $96 million contract with Buffalo that included $50 million guaranteed.

General manager Rick Smith, vice president of football administration Chris Olsen and agent Tom Condon reached an agreement in principle on the record-setting extension late Monday night, according to people familiar with the negotiations. They worked all day Monday and into the night to complete the deal before the Texans begin practice for Sunday’s regular-season opener against the Washington Redskins.

Watt, 25, will sign Tuesday, and a there will be a news conference at NRG Stadium.

Watt, the 11th overall pick in the 2011 draft, had two years left on his contract, including a base salary of $1.9 million this year and a $6.9 option year in 2015.

Under the terms of his extension, Watt’s base salaries this year and in 2015 will be $907,385 and $9.969 million. When he signs, he gets $10 million.

Watt’s new deal begins in 2016 and extends through the 2021.

The two sides had been involved in negotiations for several weeks. Before the Texans began the first of three joint practices at Denver, Watt went public with his desire for an extension.

Condon had been working under a deadline. Smith has a policy against contract negotiations in regular season because he believes they are a distraction.

Watt, who was voted NFL Defensive Player of the Year in 2012 and is considered to be the league’s premier defensive player, had no leverage.

Watt had two years left on his contract, and the Texans could have used the franchise tag on him after that. They redid his deal because he’s a great player who outplayed his original contract.

The Texans usually negotiate extensions for their best players when they have one year left on their contract. But they make exceptions for their elite players like Watt and Andre Johnson.

Johnson is the only other Texans to have his contract redone with more than one year remaining.