In 1943 and 1944 Bogart went on War effort tours with his third wife Mayo Methot, making trips to Italy and North Africa. He produced shorts for The American Red Cross effort and the Victory Bond drive. The relationship with Mayo was strained. She accused Bogart of having an affair with Ingrid Bergman during the filming of Casablanca. Bergman later remembered that Bogart barely spoke to her off camera, let alone had an affair.

Back stateside, Bogart was cast as Steve Morgan for an adaptation of Ernest Hemingway’s To Have and Have Not.

In casting "Slim" Browning, Howard Hawks’ wife Nancy Keith saw a Harper’s Bazaar cover that featured an eighteen year-old model and actress named Betty Joan Perske. Hawks immediately signed her to a contract. She’d soon change her name to Lauren Bacall.

Mayo Methot had long accused Bogart of affairs with all his co-stars, something he’d actually never done. When Bogie and Bacall met, he was attracted to her outspoken personality, poise, looks, and long, lean figure.

Bogart kept Bacall at ease during filming and their chemistry was apparent from the beginning, with their twenty-five year age difference creating a mentor-student acting dynamic.

At first Bogart made sure his meetings with her were discreet and brief. They wrote heart-felt letters and made sure to be publicly professional, while Bogart encouraged her to steal scenes, delighting Howard Hawks. But when Hawks realized there was more to their chemistry than friendship, he disapproved of the affair.

The film premiered on October 11th, 1944 while Bogart refused to stop seeing Bacall. His marriage to Mayo Methot was finally over. He filed for divorce in February of 1945.

The next month, Bogart appeared on the Thursday March 8th 1945 episode of Suspense in Bill Spier’s production of “Love’s Lovely Counterfeit” at 8PM eastern time. This episode had a rating of 13.6, winning its time slot against NBC’s Frank Morgan Show. Playing opposite Bogart was Lurene Tuttle.

Bogart and Lauren Bacall married in a small ceremony at the country home of Bogart's close friend, Pulitzer Prize-winning author Louis Bromfield, on May 21st, 1945.

On August 30th, the couple appeared with Frank Sinatra on Command Performance.