The 27-year-old told the court about the night leading up to Steenkamp's death and how the shooting occurred back in the early hours of Valentine's Day morning last year.
Pistorius claimed that he fell asleep between 9pm and 10pm alongside his girlfriend, but woke up in the early hours of February 14 to move the fans as it was 'extremely warm'.
He continued by telling the court that "everything changed" when he heard the bathroom window slide open and that he immediately thought that a burglar had entered his home.
Pistorius claimed that his first thought was to grab the firearm by his bed in order to "protect" Steenkamp and himself from who he thought was an intruder.
According to the double amputee, he began shouting at the person in the bathroom to leave his home as he was 'overcome with fear', while also yelling to Steenkamp to call the police.
While speaking to the court, Pistorius broke down in tears when an image of Steenkamp's head injury flashed up on the screen.
The athlete denies murder by maintaining that he mistook Steenkamp for a burglar when he fired four gunshots through the toilet door.