Aśoka is born a son of Bindusara, the ruler of the Mauryan Empire at the time. He had several other brothers as well, and wasn't favored over them.
Viceroy of Avanti Province
He was sent to help rule the province as soon as he was old enough.
Battle for the throne
272 BCE - 270 BCE
Immediately following Bindusara's death, was a two year battle between Aśoka and his brothers. It was known to be very brutal, and thought that Aśoka killed almost all his brothers for the throne. Whatever happened, Aśoka finished victorious and assumed the throne.
Death of Bindusara
Aśoka is coronated
After winning the battle, Aśoka had to wait a few years before being officially coronated as the third emperor of the Mauryan Empire.
After seeing the aftermath of the battle of Kalinga, Aśoka turned to Buddhism because he wanted to cause less suffering.
The battle of Kalinga
To continue expanding his empire, Aśoka attacked Kalinga, and, though with a great amount of bloodshed, he successfully conquered it.
250 BCE - 240 BCE
Between 250 BCE and 240 BCE, he built what are now known as the pillars of Aśoka, which were 40-50 foot tall columns of stone engraved with a message from him. They detailed his policies and dreams for the empire, focusing on the well-being of all his subjects.
Aśoka died and ended his rule as emperor of the Mauryan Empire, leaving the throne to his Grandson. He left behind wells, roads, hospitals, the Royal Road, many new Buddhists, and was followed by almost 40 years of peace.