Leo was selling illegal drugs to other teenagers at a club until he was brought to the White House due to the Capitol bombing. He was then told to watch his younger sister Penny while his parents were left to deal with the attack. When asked if their father was scared, Leo replied that he wasn't scared of anything.
Unfortunately for Leo, his mother Alex found out about his illegal activities when Penny found a bag of drugs in their drawer. As a result, he received a lecture.
There was uncertainty as to Leo's parentage - his mother was dating another man when she met and fell in love with Tom Kirkman, and subsequently it was unclear who Leo's biological father was. When a journalist investigated the situation, Tom Kirkman took a paternity test. Leo eventually decided he didn't care who his biological father was, becaues Tom is his dad and gave the test result back to Tom without looking at it. It was revealed Tom was indeed Leo's biological father.
In Season 2 it was revealed Leo applied to Stanford University without telling his father. When Leo was accepted at both Georgetown and Stanford he decided to stay in Washington to be close to his father and sister, after Alex's death. Tom encouraged Leo to choose the university he most wanted to go. Leo chose to go to Stanford.