Morihei Ueshiba was born in Nishinotani village (now part of the city of Tanabe), Wakayama Prefecture, Japan, on December 14, 1883, the fourth child (and only son) born to Yoroku Ueshiba and his wife Yuki.

Ueshiba studied several martial arts during his early life, and was renowned for his physical strength during his youth. During his sojourn in Tokyo he studied Kitō-ryū jujutsu under Takisaburo Tobari, and briefly enrolled in a school teaching Shinkage-ryū. His training in Gotō-ha Yagyū-ryu under Masakatsu Nakai was sporadic due to his military Service, although he was granted a diploma in the art within a few years. In 1901 he received some instruction from Tozawa Tokusaburōin in Tenjin Shin'yō-ryū jujutsu and he studied judo with Kiyoichi Takagi in Tanabe in 1911, after his father had a dojo built on the family compound to encourage his son's training. In 1907, after his return from the war, he was also presented with a certificate of enlightenment (shingon inkyo) by his childhood Teacher Mitsujo Fujimoto.

In 1903, Ueshiba was called up for military Service. He failed the initial physical examination, being shorter than the regulation 5 feet 2 inches (1.57 m). To overcome this, he stretched his spine by attaching heavy weights to his legs and suspending himself from tree branches; when he re-took the physical exam he had increased his height by the necessary half-inch to pass. He was assigned to the Osaka Fourth Division, 37th Regiment, and was promoted to corporal of the 61st Wakayama regiment by the following year; after serving on the front lines during the Russo-Japanese War he was promoted to sergeant. He was discharged in 1907, and again returned to his father's farm in Tanabe. Here he befriended the Writer and Philosopher Minakata Kumagusu, becoming involved with Minakata's opposition to the Meiji government's Shrine Consolidation Policy. He and his wife had their first child, a daughter named Matsuko, in 1911.

The son of a landowner from Tanabe, Ueshiba studied a number of martial arts in his youth, and served in the Japanese Army during the Russo-Japanese War. After being discharged in 1907, he moved to Hokkaidō as the head of a pioneer settlement; here he met and studied with Takeda Sōkaku, the founder of Daitō-ryū Aiki-jūjutsu. On leaving Hokkaido in 1919, Ueshiba joined the Ōmoto-kyō movement, a Shinto sect, in Ayabe, where he served as a martial arts instructor and opened his first dojo. He accompanied the head of the Ōmoto-kyō group, Onisaburo Deguchi, on an expedition to Mongolia in 1924, where they were captured by Chinese troops and returned to Japan. The following year, he had a profound spiritual experience, stating that, "a golden spirit sprang up from the ground, veiled my body, and changed my body into a golden one." After this experience, his martial arts skill appeared to be greatly increased.

In the early part of the 20th century, the prefectural government of Hokkaidō, Japan's northernmost island, were offering various grants and incentives for mainland Japanese groups willing to relocate there. At the time, Hokkaidō was still largely unsettled by the Japanese, being occupied primarily by the indigenous Ainu. In 1910, Ueshiba travelled to Hokkaidō in the company of his acquaintance Denzaburo Kurahashi, who had lived on the northern island before. His intent was to scout out a propitious location for a new settlement, and he found the site at Shirataki suitable for his plans. Despite the hardships he suffered on this journey (which included getting lost in snowstorms several times and an incident in which he nearly drowned in a freezing river), Ueshiba returned to Tanabe filled with enthusiasm for the project, and began recruiting families to join him. He became the leader of the Kishū Settlement Group, a collective of eighty-five pioneers who intended to settle in the Shirataki district and live as farmers; the group founded the village of Yubetsu (later Shirataki village) in August, 1912. Much of the funding for this project came from Ueshiba's father and his brothers-in-law Zenzo and Koshiro Inoue. Zenzo's son Noriaki was also a member of the settlement group.

The young Ueshiba met Takeda Sōkaku, the founder of Daitō-ryū Aiki-jūjutsu, at the Hisada Inn in Engaru, in March 1915. Ueshiba was deeply impressed with Takeda's martial art, and despite being on an important mission for his village at the time, abandoned his journey to spend the next month studying with Takeda. He requested formal instruction and began studying Takeda's style of jūjutsu in earnest, going so far as to construct a dojo at his home and inviting his new Teacher to be a permanent house guest. He received a kyōju dairi certificate, a teaching license, for the system from Takeda in 1922, when Takeda visited him in Ayabe. Takeda also gave him a Yagyū Shinkage-ryū sword transmission scroll. Ueshiba then became a representative of Daitō-ryū, toured with Takeda as a teaching assistant and taught the system to others. The relationship between Ueshiba and Takeda was a complicated one. Ueshiba was an extremely dedicated student, dutifully attending to his teacher's needs and displaying great respect. However, Takeda overshadowed him throughout his early martial arts career, and Ueshiba's own students recorded the need to address what they referred to as "the Takeda problem".

Poor soil conditions and bad weather led to crop failures during the first three years of the project, but the group still managed to cultivate mint and farm livestock. The burgeoning timber industry provided a boost to the settlement's economy, and by 1918 there were over 500 families residing there. A fire in 1917 razed the entire village, leading to the departure of around twenty families. Ueshiba was attending a meeting over railway construction around 50 miles away, but on learning of the fire travelled back the entire distance on foot. He was elected to the village council that year, and took a prominent role in leading the reconstruction efforts. In the summer of 1918, Hatsu gave birth to their first son, Takemori.

In November 1919, Ueshiba learned that his father Yoroku was ill, and was not expected to survive. Leaving most of his possessions to Takeda, Ueshiba left Shirataki with the apparent intention of returning to Tanabe to visit his ailing parent. En route he made a detour to Ayabe, near Kyoto, intending to visit Onisaburo Deguchi, the spiritual leader of the Ōmoto-kyō religion (Ueshiba's nephew Noriaki Inoue had already joined the religion and may have recommended it to his uncle). Ueshiba stayed at the Ōmoto-kyō headquarters for several days, and met with Deguchi, who told him that, "There is nothing to worry about with your father". On his return to Tanabe, Ueshiba found that Yoroku had died. Criticised by family and friends for arriving too late to see his father, Ueshiba went into the mountains with a sword and practised solo sword exercises for several days; this almost led to his arrest when the police were informed of a sword-wielding MadMan on the loose.

The technical curriculum of aikido was derived from the teachings of Takeda Sōkaku; the basic techniques of aikido stem from his Daitō-ryū system. In the earlier years of his teaching, from the 1920s to the mid-1930s, Ueshiba taught the Daitō-ryū Aiki-jūjutsu system; his early students' documents bear the term Daitō-ryū. Indeed, Ueshiba trained one of the Future highest grade earners in Daitō-ryū, Takuma Hisa, in the art before Takeda took charge of Hisa's training.

There were roughly four generations of students, comprising the pre-war students (training c.1921–1935), students who trained during the Second World War (c.1936–1945), the post-war students in Iwama (c.1946–1955) and the students who trained with Ueshiba during his final years (c.1956–c.1969). As a result of Ueshiba's martial development throughout his life, students from each of these generations tend to have markedly different approaches to aikido. These variations are compounded by the fact that few students trained with Ueshiba for a protracted period; only Yoichiro Inoue, Kenji Tomiki, Gozo Shioda, Morihiro Saito and Tsutomu Yukawa studied directly under Ueshiba for more than five or six years. After the war, Ueshiba and the Hombu Dojo dispatched some of their students to various other countries, resulting in aikido spreading around the world.

Three years later, in 1924, Deguchi led a small group of Ōmoto-kyō disciples, including Ueshiba, on a journey to Mongolia at the invitation of retired naval captain Yutaro Yano and his associates within the ultra-nationalist Black Dragon Society. Deguchi's intent was to establish a new religious kingdom in Mongolia, and to this end he had distributed propaganda suggesting that he was the reincarnation of Genghis Khan. Allied with the Mongolian bandit Lu Zhankui, Deguchi's group were arrested in Tongliao by the Chinese authorities—fortunately for Ueshiba, whilst Lu and his men were executed by firing squad, the Japanese group were released into the custody of the Japanese consul. They were returned under guard to Japan, where Deguchi was imprisoned for breaking the terms of his bail. During this expedition Ueshiba was given the Chinese alias Wang Shou-gao, rendered in Japanese as "Moritaka" – he was reportedly very taken with this name and continued to use it intermittently for the rest of his life.

During his lifetime, Ueshiba had three spiritual experiences that impacted greatly on his understanding of the martial arts. The first occurred in 1925, after Ueshiba had defeated a naval officer's bokken (wooden katana) attacks unarmed and without hurting the officer. Ueshiba then walked to his garden, where he had the following realisation:

In 1926 Takeshita invited Ueshiba to visit Tokyo again. Ueshiba relented and returned to the capital, but while residing there was stricken with a serious illness. Deguchi visited his ailing student and, concerned for his health, commanded Ueshiba to return to Ayabe. The appeal of returning increased after Ueshiba was questioned by the police following his meeting with Deguchi; the authorities were keeping the Ōmoto-kyō leader under close surveillance. Angered at the treatment he had received, Ueshiba went back to Ayabe again. Six months later, this time with Deguchi's blessing, he and his family moved permanently to Tokyo. This move allowed Ueshiba to teach politicians, high-ranking military personnel, and members of the Imperial household; suddenly he was no longer an obscure provincial martial Artist, but a sensei to some of Japan's most important citizens. Arriving in October 1927, the Ueshiba family set up home in the Shirokane district. The building proved too small to house the growing number of aikido students, and so the Ueshibas moved to larger premises, first in Mita district, then in Takanawa, and finally to a purpose-built hall in Shinjuku. This last location, originally named the Kobukan (皇武館), would eventually become the Aikikai Hombu Dojo. During its construction, Ueshiba rented a property nearby, where he was visited by Kanō Jigorō, the founder of judo.

The 1930s saw Japan's invasion of mainland Asia and increased military activity in Europe. Ueshiba was concerned about the prospect of war, and became involved in a number of efforts to try and forestall the conflict that would eventually become World War II. He was part of a group, along with Shūmei Ōkawa and several wealthy Japanese backers, that tried to broker a deal with Harry Chandler to export aviation fuel from the United States to Japan (in contravention of the oil embargo that was currently in force), although this effort ultimately failed. In 1941 Ueshiba also undertook a secret diplomatic mission to China at the behest of Prince Fumimaro Konoe. The intended goal was a meeting with Chiang Kai-shek to establish peace talks, but Ueshiba was unable to meet with the Chinese leader, arriving too late to fulfil his mission.

In 1932, Ueshiba's daughter Matsuko was married to the swordsman Kiyoshi Nakakura, who was adopted as Ueshiba's heir under the name Morihiro Ueshiba. The marriage ended after a few years, and Nakakura left the family in 1937. Ueshiba later designated his son Kisshomaru as the heir to his martial art.

From 1935 onwards, Ueshiba had been purchasing land in Iwama in Ibaraki Prefecture, and by the early 1940s had acquired around 17 acres (6.9 ha; 0.027 sq mi) of farmland there. In 1942, disenchanted with the war-mongering and political manoeuvring in the capital, he left Tokyo and moved to Iwama permanently, settling in a small farmer's cottage. Here he founded the Aiki Shuren Dojo, also known as the Iwama dojo, and the Aiki Shrine, a devotional shrine to the "Great Spirit of Aiki". During this time he travelled extensively in Japan, particularly in the Kansai region, teaching his aikido. Despite the prohibition on the teaching of martial arts after World War II, Ueshiba and his students continued to practice in secret at the Iwama dojo; the Hombu dojo in Tokyo was in any case being used as a refugee centre for citizens displaced by the severe firebombing. It was during this period that Ueshiba met and befriended Koun Nakanishi, an expert in kotodama. The study of kotodama was to become one of Ueshiba's passions in later life, and Nakanishi's work inspired Ueshiba's concept of takemusu aiki.

His second experience occurred in 1940 when engaged in the ritual purification process of misogi.

After these events, Ueshiba seemed to slowly grow away from Takeda, and he began to change his art. These changes are reflected in the differing names with which he referred to his system, first as aiki-jūjutsu, then Ueshiba-ryū, Asahi-ryū, and aiki budō. In 1942, when Ueshiba's group joined the Dai Nippon Butoku Kai, the martial art that Ueshiba developed finally came to be known as aikido.

The government prohibition (on aikido, at least) was lifted in 1948 with the creation of the Aiki Foundation, established by the Japanese Ministry of Education with permission from the Occupation forces. The Hombu dojo re-opened the following year. After the war Ueshiba effectively retired from aikido. He delegated most of the work of running the Hombu dojo and the Aiki Federation to his son Kisshomaru, and instead chose to spend much of his time in prayer, meditation, calligraphy and farming. He still travelled extensively to promote aikido, even visiting Hawaii in 1961. He also appeared in a television documentary on aikido: NTV's The Master of Aikido, broadcast in January 1960. Ueshiba maintained links with the Japanese nationalist movement even in later life; his student Kanshu Sunadomari reported that Ueshiba temporarily sheltered Mikami Taku, one of the naval officers involved in the May 15 Incident, at Iwama.

In 1969, Ueshiba became ill. He led his last training session on March 10, and was taken to hospital where he was diagnosed with cancer of the liver. He died suddenly on April 26, 1969. His body was buried at Kōzan-ji, and he was given the posthumous Buddhist title "Aiki-in Moritake En'yū Daidōshi" (合気院盛武円融大道士); parts of his hair were enshrined at Ayabe, Iwama and Kumano. Two months later, his wife Hatsu (植芝 はつ Ueshiba Hatsu, née Itokawa Hatsu; 1881–1969) also died.

Aikido—usually translated as the Way of Unifying Spirit or the Way of Spiritual Harmony—is a fighting system that focuses on throws, pins and joint locks together with some striking techniques. It emphasises protecting the opponent and promotes spiritual and social development.