On the October 17 episode of SmackDown, Styles began a rivalry with then WWE Champion, Jinder Mahal, by confronting and attacking him.
On October 22, Styles appeared at Raw's exclusive event TLC: Tables, Ladders & Chairs, competing against Finn Bálor due to Bálor's original opponent Bray Wyatt not being cleared to compete, where he was defeated by Bálor.
On the November 7 episode of SmackDown in Manchester, England, Styles defeated Jinder Mahal to win the WWE Championship for the second time in what marked the first time the title changed hands on SmackDown since September 2003, becoming recognized by WWE as the first titleholder crowned outside of North America (Antonio Inoki had won the title in Japan in 1979, but this reign is unrecognized by WWE).
With the win, Styles replaced Mahal in the champion vs. champion match at Survivor Series against Universal Champion Brock Lesnar, which he would go on to lose.
At Clash of Champions on December 17, Styles defeated Mahal via submission in his first title defense.
Styles' next feud came against Kevin Owens and Sami Zayn, whom he lost back-to-back matches to due to interference, which led to a handicap championship match at the Royal Rumble on January 28, 2018 which Styles won.
Styles then successfully defended the title against Kevin Owens, Sami Zayn, John Cena, Baron Corbin, and Dolph Ziggler in a six-pack challenge at Fastlane on March 11.

Shortly after, Styles started a feud with Royal Rumble winner Shinsuke Nakamura.
At WrestleMania 34 on April 8, Styles defeated Nakamura to retain the WWE Championship, and after the match, Styles was subjected to a classless assault by Nakamura, heating up their feud.
Styles would go on to retain his title against Nakamura on three different events: Greatest Royal Rumble by double countout, Backlash in a no disqualification match, that ended in a no contest, and Money in the Bank, where Styles ended the feud after winning a Last Man Standing match.
After a successful defense against Rusev at Extreme Rules in July, Styles became the longest-reigning WWE Champion in SmackDown history on August 14, surpassing the 280-day record set by John "Bradshaw" Layfield.
On the July 24 episode of SmackDown, Styles started a feud with Samoa Joe, after he was attacked by Joe.
Styles retained the title at SummerSlam, despite losing via disqualification.
Styles' and Joe's rivalry continued following SummerSlam over Styles' wife, Wendy, where Joe claimed he would defeat Styles and become the "new daddy", leading to a rematch at Hell in a Cell, where Styles defeated Joe in controversial fashion to retain the title; Styles submitted to Joe during a roll-up, however, the referee did not see the submission and counted the pin allowing Styles to retain the title.
Styles defeated Joe two more times at Super Show-Down by submission and Crown Jewel.

At Super Show-Down, Daniel Bryan become the number one contender for Styles' title, they would be scheduled to face each other for the title at Crown Jewel.
However, the match took place on the October 30 episode of SmackDown Live, where Styles defeated Bryan to retain the title.
On November 7, Styles surpassed the 365-day mark of his title reign, becoming the 8th man to have held the WWE Championship for a continuous reign of a full year.
On the November 13 episode of SmackDown Live, Styles lost his title to Daniel Bryan following a low blow, ending his reign at 371 days.
Styles received his rematch against Bryan at TLC: Tables, Ladders & Chairs, but failed to regain the championship.
On the October 17 episode of SmackDown, Styles began a rivalry with then WWE Champion, Jinder Mahal, by confronting and attacking him. On October 22, Styles appeared at Raw's exclusive event TLC: Tables, Ladders & Chairs, competing against Finn Bálor due to Bálor's original opponent Bray Wyatt not being cleared to compete, where he was defeated by Bálor. On the November 7 episode of SmackDown in Manchester, England, Styles defeated Jinder Mahal to win the WWE Championship for the second time in what marked the first time the title changed hands on SmackDown since September 2003, becoming recognized by WWE as the first titleholder crowned outside of North America (Antonio Inoki had won the title in Japan in 1979, but this reign is unrecognized by WWE). With the win, Styles replaced Mahal in the champion vs. champion match at Survivor Series against Universal Champion Brock Lesnar, which he would go on to lose. At Clash of Champions on December 17, Styles defeated Mahal via submission in his first title defense. Styles' next feud came against Kevin Owens and Sami Zayn, whom he lost back-to-back matches to due to interference, which led to a handicap championship match at the Royal Rumble on January 28, 2018 which Styles won. Styles then successfully defended the title against Kevin Owens, Sami Zayn, John Cena, Baron Corbin, and Dolph Ziggler in a six-pack challenge at Fastlane on March 11.
Shortly after, Styles started a feud with Royal Rumble winner Shinsuke Nakamura. At WrestleMania 34 on April 8, Styles defeated Nakamura to retain the WWE Championship, and after the match, Styles was subjected to a classless assault by Nakamura, heating up their feud. Styles would go on to retain his title against Nakamura on three different events: Greatest Royal Rumble by double countout, Backlash in a no disqualification match, that ended in a no contest, and Money in the Bank, where Styles ended the feud after winning a Last Man Standing match. After a successful defense against Rusev at Extreme Rules in July, Styles became the longest-reigning WWE Champion in SmackDown history on August 14, surpassing the 280-day record set by John "Bradshaw" Layfield. On the July 24 episode of SmackDown, Styles started a feud with Samoa Joe, after he was attacked by Joe. Styles retained the title at SummerSlam, despite losing via disqualification. Styles' and Joe's rivalry continued following SummerSlam over Styles' wife, Wendy, where Joe claimed he would defeat Styles and become the "new daddy", leading to a rematch at Hell in a Cell, where Styles defeated Joe in controversial fashion to retain the title; Styles submitted to Joe during a roll-up, however, the referee did not see the submission and counted the pin allowing Styles to retain the title. Styles defeated Joe two more times at Super Show-Down by submission and Crown Jewel.
At Super Show-Down, Daniel Bryan become the number one contender for Styles' title, they would be scheduled to face each other for the title at Crown Jewel. However, the match took place on the October 30 episode of SmackDown Live, where Styles defeated Bryan to retain the title. On November 7, Styles surpassed the 365-day mark of his title reign, becoming the 8th man to have held the WWE Championship for a continuous reign of a full year. On the November 13 episode of SmackDown Live, Styles lost his title to Daniel Bryan following a low blow, ending his reign at 371 days. Styles received his rematch against Bryan at TLC: Tables, Ladders & Chairs, but failed to regain the championship.
A.J. Styles