Hiashi was born seconds before his twin brother Hizashi, making Hiashi the head of Hyuga clan and Hizashi the member of a branch house, whose only purpose in life would be to protect members of the main house. Years later when Neji was born, Hizashi became bitter that his son would never be able to reach his full potential as a member of the main house, causing him to be openly resentful of Hiashi and his daughters. Hiashi then being the one to brand Neji with the Hyuga Main Family's Juinjutsu further strained the relationship between the two brothers.
During a visit to Konoha by a Head Ninja of Kumogakure no sato, who came to the village to sign a peace treaty, a young Hinata was kidnapped. Hiashi saved her by killing her kidnapper, only to discover that it was the Kumogakure ambassador. Kumogakure demanded Hiashi's head in return for the life he took or risk resuming open warfare between the two villages. Konoha, wishing to avoid another conflict, was compelled to comply, but was not willing to fulfill Kumogakure's desires of getting to study the Byakugan. The Hyuga clan elders suggested that Hizashi be used as a body double since his cursed seal would seal off his Byakugan upon his death. Although Hiashi tried to find an alternative, Hizashi insisted, saying that he would finally get to choose his own fate and that he could save his brother's life. Before going to his death he asked Hiashi to someday tell Neji about why he made his decision.
Originally, Hiashi had trained Hinata to become the successor of the Hyuga Clan. Hinata's lack of confidence ultimately led him to deciding she was not worthy and instead turned his attention to his younger daughter, Hanabi, while leaving Hinata in Kurenai Yuhi's care.
Hiashi's general personality is very stern and strict, as he assigns both his daughters arduous training, rarely complimenting their performance. This is especially true with Hinata; when she was assigned to Kurenai Yuhi, he told her that he was unconcerned about the possibility that she would die, saying that the Hyuga Clan had no use for a weak successor. In truth, it was not that he felt Hinata's talent or potential was weak, but her drive to succeed was too weak to be the successor of the Hyuga Clan. As the series progresses and she starts to her show her true dedication, he begins to openly cheer her on.
Hiashi makes his debut with Hanabi watching Neji's match during the final rounds of the Chunin Exams. He is amazed that Neji has been able to learn the main house's secret techniques by himself, but is disappointed by Neji's resentment of the main house and his strong belief in fate. After Neji loses to Naruto, and Neji seemed to have found himself at a crossroads in his life from Naruto's words, Hiashi decided to tell him about the circumstances surrounding Hizashi's death. Although Neji did not initially believe him, Hiashi's bowing to him for forgiveness showed him that it was true.
Hiashi assists in the defense of Konoha during the invasion by Sunagakure and Otogakure]], repelling invaders with Eight Trigrams Palms Heavenly Spin. In the anime's filler arcs Hiashi, realizing separating the Hyuga clan into two houses was causing a huge rift in the clan, decided, as head of the clan, to try and mend this. He began training Neji regularly in their clan's full arts, something that was already considered a taboo by the rest of the Main House. His relationship with Hinata is seen improving, as he encourages her to do her best after seeing her more confident in herself.
As the a member of the Hyuga clan, Hiashi possesses the Byakugan, which gives him an almost 360-degree field of vision, except for a small blind spot at the back of the neck. Also, as the head of his clan, he is well-versed in all of his clan's secret techniques. While the full extent of his prowess remains unknown, during Orochimaru's invasion, Hiashi demonstrated tremendous skill by repelling several Sound and Sand ninja away with one Eight Trigrams Palms Heavenly Spin.