Chancellor was born on April 3, 1988 in Norfolk, Virginia to Karen Lambert. Chancellor's mother always had about two or three jobs all the time and there were five siblings all living together. He never had much money growing up and his family made sure he and his siblings stayed off the street and away from violence.
Chancellor attended Matthew Fontaine Maury High School where he played basketball and football as a quarterback and safety for the Commodores athletic teams. As a senior in 2005, he recorded more than 2,000 passing yards and 500 rushing yards and led his team to a 10–2 record and an appearance in the Group AAA Division 5 playoffs. Chancellor was named the team's most valuable player, and he was also placed on the All-Eastern District first team as well as The Virginian-Pilot All-Tidewater second team. Rivals.com assessed him as the 27th-ranked pro-style quarterback prospect in the nation and the 20th-ranked player in the state of Virginia. SuperPrep and The Roanoke Times rated him the 21st-ranked player in the state. The Scout.com recruiting site assessed Chancellor as a two-star recruit and he accepted a scholarship offer from Virginia Tech.
Chancellor enrolled at Virginia Tech in 2006 to study human development. He worked out as a quarterback before eventually being moved to the cornerback position prior to the start of the season. He saw action that year as a true freshman in all 13 games, and recorded nine tackles, two broken up passes, and one interception.
In 2007, he was moved to the rover position as the starter and also played on special teams. He started in all 14 games and recorded 79 tackles, seven broken-up passes, three quarterback hurries, and one interception as a sophomore.
Before the 2008 season, Chancellor was moved to the free safety position, his third position change in three of four years at Virginia Tech. Chancellor started in all 14 games and recorded 52 tackles, of which 27 were solo, two interceptions, five broken-up passes, seven pass deflections, one forced fumble, and two fumble recoveries. After the season, he considered entering the 2009 NFL Draft a year early, but decided to remain at Virginia Tech for his senior season.
Before his senior season, Hokies' defensive backs coach, Torrian Gray said that Chancellor could be "the greatest safety in Virginia Tech history. In his senior season, Chancellor recorded two interceptions, one fumble return, 68 total tackles, three tackles-for-loss, and four broken-up passes. Chancellor has said that he attempts to emulate the former Washington Redskins safety Sean Taylor, and said, "[He was a] big safety, the prototype guy for the position. I'm a big safety, too, and I've just always wanted to be just like him. I don't necessarily say I can be Sean Taylor before it's over, but I think I can be just as good." Also, before games and when he needs motivation, Chancellor says he watched the highlights of Sean Taylor on YouTube. He says it motivated him to do better, strive for greater things, and took him to a darker place which makes him play better. The CBS Sports-affiliated NFL Draft Scout considered Chancellor the third-ranked of the 126 free safeties available for the 2010 NFL Draft and projected him as a third-round selection.
Chancellor was drafted by the Seattle Seahawks early in the fifth round with the 133rd overall pick in the 2010 NFL Draft.
Chancellor did not start a game in his rookie season, but did record meaningful statistics in seven games.
Chancellor began the 2011 season as the team's starting strong safety, replacing recently unsigned veteran Lawyer Milloy on the depth chart. Chancellor had a very strong season, coming in second on the team in both tackles and interceptions. As a result, he was added to the 2012 Pro Bowl roster, replacing Dashon Goldson of the San Francisco 49ers.
The 2012 season saw Chancellor as the incumbent starting strong safety, and he started all 16 games. He did not record any sacks or interceptions for the season, though he did have a career-high 101 tackles.
In April 2013, Chancellor agreed to a four-year extension worth up to $28 million with the Seahawks, placing him under contract through 2017.
In the 2013 season, Chancellor recorded 65 tackles and three interceptions. On February 2, 2014, the Seahawks won Super Bowl XLVIII against the Denver Broncos 43–8. Chancellor recorded an interception and nine tackles during the game.
At the start of the 2014 season, Chancellor was named a team captain, joining quarterback Russell Wilson, punter Jon Ryan, and placekicker Steven Hauschka as the Seattle Seahawks four team captains. On September 21, 2014, in a Super Bowl XLVIII rematch with the Denver Broncos, Chancellor recorded 9 tackles, an interception, a forced fumble, and 2 passes defended in a 26-20 victory, winning the NFC Defensive Player of the Week Award. At the end of the regular season he was selected for the third Pro Bowl of his career and voted in the Second-team All-Pro by the Associated Press.
In the Seahawks' Divisional Round game against the Carolina Panthers, Chancellor had a career game in which he recorded nine solo tackles, two assists, and an interception, which was returned 90 yards for a touchdown. It was his third straight postseason game with an interception. Chancellor also vaulted the Panthers' offensive line twice in attempt to block a field goal at the end of the half, though neither attempt counted due to penalties. In the NFC Championship against the Green Bay Packers, Chancellor had four tackles in the 28-22 overtime victory. In Super Bowl XLIX, Chancellor recorded 10 tackles as the Seahawks failed to repeat as Super Bowl champions. They fell to the New England Patriots 28-24.
One year into his four-year extension, Chancellor requested a new contract. As of September 14, 2015, there had been no new contract talks between Chancellor and the Seahawks. Chancellor missed the opening game of the 2015 NFL season, a 34-31 overtime loss to the St. Louis Rams. Chancellor returned to the 0-2 Seahawks in Week 3. The Seahawks went 10-4 since Chancellor's return. For his play in the 2015 season, he earned a trip to the 2016 Pro Bowl. He was ranked 32nd by his fellow players on the NFL Top 100 Players of 2016.
In the Wild Card Round of the postseason for the 2015 season, Chancellor would force a fourth quarter fumble of running back Adrian Peterson in a game against the Minnesota Vikings. The Seahawks would recover, and ultimately kick a field goal on the subsequent drive, giving the Seahawks a 10-9 lead, which would end up being the final score of the game after Blair Walsh missed a potential game-winning field goal in the final seconds. The Seahawks went on to lose in the Divisional Round to the eventual NFC Champion Carolina Panthers by a score of 31–24.
Starting the 2016 season, Chancellor was named defensive team captain for the second time in his career, joining Russell Wilson, Jon Ryan, and cornerback DeShawn Shead as the four Seahawk captains.
In the 2016 season, Chancellor had 47 tackles and two interceptions. The Seahawks would return to the playoffs. In the Wild Card Round victory against the Detroit Lions, Chancellor had six tackles. In the Divisional Round loss to the Atlanta Falcons, Chancellor had six tackles for the second consecutive playoff game. After the season, he was ranked 34th by his fellow players on the NFL Top 100 Players of 2017.
On August 1, 2017, Chancellor signed a three-year, $36 million contract extension with $25 million guaranteed with the Seahawks.
As a child, Chancellor often visited the Boys and Girls club. His goal is to restore the building to the significance it had for him in the past where there were activities and it was also a safe haven for kids to avoid the violence in the community. With his $34 million contract he signed in 2014 with the Seahawks, he bought his mother a new Lexus and a house, which were things she never had.