Leonardo "Leo" Falconeri was born during the 2015 Nurse Ball. His parents were Olivia Falconeri and Julian Jerome, but they were never in a romantic relationship. Olivia had been in love with Ned Quartermaine, and Julian had been in love with Alexis Davis, but Ned and Alexis had been romantically involved with each other.

Feeling lonely and heartbroken, Olivia and Julian had spent New Year's Eve finding comfort in each other's arms, but their tryst ended the next morning when Olivia realized that it had been a mistake to lean on someone like Julian. Julian was a notorious mobster who had gone up against mob boss Sonny Corinthos on more than one occasion.

When Olivia realized that she was pregnant, she confided her secret to Ned, but she hid the truth from Julian. Olivia worried about Julian's violent lifestyle. Ned assured Olivia that he would be there for Olivia, and he would help her raise the baby. Things had fallen apart between Ned and Alexis, so Olivia knew that Ned could offer her and the baby a good life.

On the night of the 2015 Nurses Ball, Sam McCall Morgan overheard Olivia and Ned talking about the baby, so she confronted Olivia about keeping the truth from Julian. Julian demanded to know what was going on, prompting his daughter to share the news. However, Olivia had gone into labor, and her water broke. Before the ambulance arrived, Olivia delivered a premature baby boy. Leo and Olivia were rushed to the hospital.

Doctors determined that Leo's lungs had been underdeveloped, but they were able to stabilize him. Leo was placed in the neonatal intensive care unit, and Olivia's concerns mounted when good friend, Duke Lavery, was killed in the mob war. Olivia appealed to her elder son, Detective Dante Falconeri, for help disappearing with her son. Later, Ned arranged for the baby to be moved to another hospital, and Dr. Liesl Obrecht helped Olivia fake Leo's death from sepsis. A short time later, Olivia left town to "mourn" the passing of her son, but in reality, she had joined Ned and the baby.

Olivia returned in August with a baby that she claimed was her adopted son, but everyone saw through the ruse. Ned decided to end things because he was tired of the lies. At the same time, Alexis received DNA confirmation that Julian was Leo's father. Olivia and Julian agreed to shared custody, and they moved forward. Leo developed a relationship with his father.

By 2017, Olivia and Ned had reconciled and married. Ned had always remained a constant in Leo's life, and he was the one who was there for Leo day-to-day. Julian struggled to break free from the mob, so Olivia would periodically refuse to let him see Leo. As a result, Julian drifted in and out of Leo's life until Julian was able to sever all ties to the mob.

By 2019, Julian was back in Leo's life, and spending time with his son on a regular basis.