November 9, 2018, Chastain and CGR announced a full season in the No. 42 Xfinity Series car for 2019. DC Solar, instrumental in Chastain's introduction to the team, remained on as sponsor. However, after DC Solar was raided by the FBI on December 18, 2018, the team lost the sponsorship and shut down in January. In January 2019, Chastain joined Niece Motorsports to drive the No. 45 Silverado part-time in the Truck Series, splitting the truck with Reid Wilson. On January 31, Chastain announced he would return to the No. 4 JD Motorsports ride for 30 races, replacing Blake Koch, who stepped away to focus on business ventures. For the other three races of the schedule – Daytona in February, Chicagoland in June, and Texas in November – Chastain announced he would join Kaulig Racing, driving the organization's No. 10 entry. In his first race with Niece, Chastain began the season with a third-place finish in the 2019 NextEra Energy 250. At his first ever Daytona 500, Chastain scored his first career top-ten in the Cup Series despite starting 36th in the race. During the spring, Chastain broke the all-time NASCAR record for most consecutive races run across all three national series to start a season, surpassing the mark of 22 set by Kyle Busch set in 2008. On May 10, 2019, Chastain won his first career NASCAR Gander Outdoors Truck Series race in the 2019 Digital Ally 250 at Kansas Speedway. He nearly spun out with 20 laps to go but saved the truck, later inheriting the lead from Stewart Friesen after he ran out of fuel. In June, he announced his intention to switch to Truck Series points to compete for a championship in the series. In June's M&M's 200 at Iowa, Chastain led 141 of 200 laps and swept the stages to score the win, but his truck failed post-race inspection and his victory was forfeited to Brett Moffitt under NASCAR's newly-introduced disqualification policy. Chastain was the first driver to have a win revoked since Dale Jarrett was disqualified from a Busch Series race in 1995, relegated to last in the official standings. Chastain's team appealed the penalty, though it was eventually upheld after a hearing with National Motorsports Appeals panelist Bryan Moss. He earned redemption the following week in Gateway's CarShield 200, however, leading 21 laps and scoring the victory after taking only fuel and no