The 2019 season started on a positive note for Johnson, as he won the 2019 Advance Auto Parts Clash after contact between him and Paul Menard sent Menard spinning while battling for the lead and triggering "The Big One" on lap 55 right before the rain arrived. It was also the first race with new sponsor Ally Financial and crew chief Meendering. He followed it up by finishing 8th in the first duel race. In the Daytona 500, Johnson ran up front most of the race, but when he came to pit road with around 40 to go, B. J. McLeod and Cody Ware's cars spun behind him and hit him in the left rear. The contact ripped off the left rear quarter-panel. He recovered to finish 9th after being 2 laps down. The next race at Atlanta Motor Speedway, Jimmie finished 24th, two laps down. He followed up by finishing 19th. He followed up that performance with a ninth-place finish. On March 29 in O'Reilly Auto Parts 500 qualifying at Texas, Johnson got his first pole since 2016 at Texas and scored his first top-five finish since the 2018 Coca-Cola 600 two days later. At the Coca-Cola 600, Johnson ran well, and ended up finishing 8th place. At Chicagoland speedway, Johnson started 4th and took the lead on lap 7 from Austin Dillon. He went on to finish fourth place followed by a 3rd-place result at the rain-shortened Coke Zero Sugar 400 a week later, his best finishes of the season.
On July 29, 2019, following a string of disappointing finishes during the season, Hendrick Motorsports announced that race engineer Cliff Daniels would replace Meendering as the crew chief of the No. 48. At Watkins Glen, Johnson finished 19th after being spun out by Ryan Blaney, leading to an argument between the two after the race. The animosity between them lasted until Michigan a week later.
In September 2019, Johnson missed the playoffs cut for the first time in his NASCAR career after finishing 35th in the Brickyard 400 due to contact with Kurt Busch that sent his car crashing hard into the wall.
On October 4, 2019, Ally extended its sponsorship of the No. 48 for three more years through the 2023 season.
On November 20, 2019, Johnson announced that the 2020 Cup season would be his last full-time season of racing, although he did not rule out a part-time schedule after that. The 2020 season started with the Daytona 500 qualifying, he finished 4th for a second year in a row. Later that day, he entered the 2020 Busch Clash as the defending champion. He started 16th and finished 11th after a tire spun on the first restart in overtime. Next race was the 2020 Bluegreen Vacations Duels. He started and finished 2nd behind team-mate William Byron in Duel 2. In his last Daytona 500, he started 6th and finished 35th after Kyle Busch and Brad Keselowski triggered "The Big One". Next week in Las Vegas, he finished 1st in the final practice. He started 18th and finished 5th in the race. At his home track Auto Club, he qualified 2nd, losing the pole position to Clint Bowyer by 0.007 seconds. In the race, his wife and children waved the green flag at the start of the race. There was a four wide salute before the race to honor him. For most of the event, he was in the Top 10 and led 10 laps; he finished 7th.
Johnson is a triathlete, regularly participating in triathlons and long-distance running; the Jimmie Johnson Foundation's Wellness Challenge also hosts triathlons. In 2019, he competed in the Boston Marathon, finishing with a time of 3:09:07 and 4,155th overall (3,746th among males and 641st in the Male 40–44 class).
Up until 2019, Johnson was the only driver to have qualified for the NASCAR Cup Series playoffs every single year since its inception in 2004. He also holds the record for the most consecutive and total playoffs appearances, with 15.