Nagahide was born in what is now Nishi-ku, Nagoya, but then part of Aichi District, Owari Province.
From his youth, Nagahide served Oda Nobunaga and became one of his senior retainers, going on to fight in the Oda clan's major battles, including Anegawa in 1570, Nagashino in 1575, the Honganji Campaign from 1570-1580, Tedorigawa in 1577, and the Second Invasion of Iga in 1581 and was named one of the administrators of Kyoto after Nobunaga entered that city in 1568.

He stayed by Nobunaga's side when his brother defied him during the Battle of Inō.
Nagahide also had military service during the Battle of Okehazama, but he wasn't a part of the main strike force.
During the Battle of Kannonji Castle, he contributed in the conquest of Ōmi Province and was a part of Nobunaga's personal formation.
His participation made him favored by his master.
According to the Nobunaga Kōki, he also served in the Mino campaign against Saitō Tatsuoki, the Ikko-ikki campaign, Nobunaga's Kyushu campaign, and the Battle of Nagashino, he also fought in the Battle of Tedorigawa under Shibata Katsuie againts Uesugi Kenshin.

When he wasn't in battle, he was aiding Nobunaga's conquests by taking care of political affairs and was the building magistrate for Azuchi castle.
One of the characters of his family name was said to have been granted for the Hashiba name for Hideyoshi.
His participation made him favored by Nobunaga, among many of other deeds.
The extent of Nobunaga's trust can be seen by the fact that Nagahide married Nobunaga's niece, while his son was Niwa Nagashige.
These services let Nagahide rule over the fief of Obama in Wakasa Province, and Sawayama Castle in Ōmi Province.

In 1581, in a military parade held at Kyoto before the eyes of the Emperor as well as foreign missionaries, Nagahide was given the honor of leading the procession.
In the same year, he fought in second Tensho Iga War againts Iga inhabitants.

In 1582, as Oda Nobutaka's second in command, Nagahide launched a campaign on Shikoku; but before he made any progress, Nobunaga died during an attack by Akechi Mitsuhide.
Nagahide abandoned the campaign and turned back to help Hashiba Hideyoshi avenge this by killing Mitsuhide at Battle of Yamazaki.

In 1583 at the subsequent meeting in Kiyosu Castle where the future of the Oda clan was discussed, Nagahide supported Hideyoshi's position, He also assisted Hideyoshi at the Battle of Shizugatake and gained Echizen Province and Kaga Province to rule, worth over 1,230,000 koku.
He thus became one of the most powerful retainers and daimyō.
Nagahide was born in what is now Nishi-ku, Nagoya, but then part of Aichi District, Owari Province. From his youth, Nagahide served Oda Nobunaga and became one of his senior retainers, going on to fight in the Oda clan's major battles, including Anegawa in 1570, Nagashino in 1575, the Honganji Campaign from 1570-1580, Tedorigawa in 1577, and the Second Invasion of Iga in 1581 and was named one of the administrators of Kyoto after Nobunaga entered that city in 1568.
He stayed by Nobunaga's side when his brother defied him during the Battle of Inō. Nagahide also had military service during the Battle of Okehazama, but he wasn't a part of the main strike force. During the Battle of Kannonji Castle, he contributed in the conquest of Ōmi Province and was a part of Nobunaga's personal formation. His participation made him favored by his master. According to the Nobunaga Kōki, he also served in the Mino campaign against Saitō Tatsuoki, the Ikko-ikki campaign, Nobunaga's Kyushu campaign, and the Battle of Nagashino, he also fought in the Battle of Tedorigawa under Shibata Katsuie againts Uesugi Kenshin.
When he wasn't in battle, he was aiding Nobunaga's conquests by taking care of political affairs and was the building magistrate for Azuchi castle. One of the characters of his family name was said to have been granted for the Hashiba name for Hideyoshi. His participation made him favored by Nobunaga, among many of other deeds. The extent of Nobunaga's trust can be seen by the fact that Nagahide married Nobunaga's niece, while his son was Niwa Nagashige. These services let Nagahide rule over the fief of Obama in Wakasa Province, and Sawayama Castle in Ōmi Province.
In 1581, in a military parade held at Kyoto before the eyes of the Emperor as well as foreign missionaries, Nagahide was given the honor of leading the procession. In the same year, he fought in second Tensho Iga War againts Iga inhabitants.
In 1582, as Oda Nobutaka's second in command, Nagahide launched a campaign on Shikoku; but before he made any progress, Nobunaga died during an attack by Akechi Mitsuhide. Nagahide abandoned the campaign and turned back to help Hashiba Hideyoshi avenge this by killing Mitsuhide at Battle of Yamazaki.
In 1583 at the subsequent meeting in Kiyosu Castle where the future of the Oda clan was discussed, Nagahide supported Hideyoshi's position, He also assisted Hideyoshi at the Battle of Shizugatake and gained Echizen Province and Kaga Province to rule, worth over 1,230,000 koku. He thus became one of the most powerful retainers and daimyō.
Niwa Nagahide