Timur became the head of the Barlas/Berlas tribe at the death of his father. However some accounts say he did this by helping Amir Husayn, a Qara'unas prince and de facto ruler of Western Chagatai Khanate.

Timur becomes head of Ulus Chagatay, and begins to develop Samarkand as his capital. He married Husayn's wife Saray Mulk Khanum, a descendant of Genghis Khan, allowing him to become imperial ruler of the Chaghatay tribe.

Timur began his Persian campaign with Herat, capital of the Kartid dynasty. When Herat did not surrender he reduced the city to rubble and massacred most of its citizens; it remained in ruins until Shah Rukh ordered its reconstruction. Timur then sent a General to capture rebellious Kandahar. With the capture of Herat the Kartid kingdom surrendered and became vassals of Timur; it would later be annexed outright less than a decade later in 1389 by Timur's son Miran Shah.

The Battle of the Kondurcha River was the first major battle of the Tokhtamysh–Timur war. It took place at the Kondurcha River, in the Bulgar Ulus of the Golden Horde, in what today is Samara Oblast in Russia. Tokhtamysh's cavalry tried to encircle Timur's army from the flanks. However, the Central Asian army withstood the assault, after which its sudden frontal attack put the Horde troops to flight. However, many of the Golden Horde troops escaped to fight again at Terek.

Timur then began a five-year campaign to the west in 1392, attacking Persian Kurdistan. In 1393, Shiraz was captured after surrendering, and the Muzaffarids became vassals of Timur, though prince Shah Mansur rebelled but was defeated, and the Muzafarids were annexed. Shortly after Georgia was devastated so that the Golden Horde could not use it to threaten northern Iran. In the same Year, Timur caught Baghdad by surprise in August by marching there in only eight days from Shiraz. Sultan Ahmad Jalayir fled to Syria, where the Mamluk Sultan Barquq protected him and killed Timur's envoys. Timur left the Sarbadar prince Khwaja Mas'ud to govern Baghdad, but he was driven out when Ahmad Jalayir returned. Ahmad was unpopular but got some dangerous help from Qara Yusuf of the Kara Koyunlu; he fled again in 1399, this time to the Ottomans.

By 1368, Han Chinese forces had driven the Mongols out of China. The first of the new Ming dynasty's emperors, the Hongwu Emperor, and his son, the Yongle Emperor, produced tributary states of many Central Asian countries. The suzerain-vassal relationship between Ming empire and Timurid existed for a long time. In 1394, Hongwu's ambassadors eventually presented Timur with a letter addressing him as a subject. He had the ambassadors Fu An, Guo Ji, and Liu Wei detained. Timur eventually planned to invade China. To this end Timur made an alliance with surviving Mongol tribes based in Mongolia and prepared all the way to Bukhara.

He decisively routed Tokhtamysh in the Battle of the Terek river on 15 April 1395. All the major cities of the khanate were destroyed: Sarai, Ukek, Majar, Azaq, Tana and Astrakhan. Timur's attack on the cities of the Golden Horde in 1395 produced his first Western European victims, since it caused the destruction of the Italian trading colonies (comptoirs) in Sarai, Tana and Astrakhan. During the siege of Tana, the trading communities sent representatives to treat with Timur, but the latter only used them in a ruse to reconnoiter the city. The Genoese city of Caffa on the Crimean peninsula was spared, despite being a former ally of Tokhtamysh.

The battle between Sultan Nasir-ud-Din Tughlaq allied with Mallu Iqbal and Timur took place on 17 December 1398. Indian forces had war elephants armored with chain mail and poison on their tusks. As his Tatar forces were afraid of the elephants, Timur ordered his men to dig a trench in front of their positions. Timur then loaded his camels with as much wood and hay as they could carry. When the war elephants charged, Timur set the hay on fire and prodded the camels with iron sticks, causing them to charge at the elephants, howling in pain: Timur had understood that elephants were easily panicked. Faced with the strange spectacle of camels flying straight at them with flames leaping from their backs, the elephants turned around and stampeded back toward their own lines. Timur capitalized on the subsequent disruption in the forces of Nasir-ud-Din Mahmud Shah Tughluq, securing an easy victory. Sultan of Delhi fled with remnants of his forces. Delhi was sacked and left in ruins. After the battle, Timur installed Khizr Khan, the Governor of Multan as the new Sultan of Delhi Sultanate under his suzerainty. Delhi's conquest was one of the greatest victories of Timur, arguably surpassing Darius the Great, Alexander the Great and Genghis Khan because of the harsh conditions of the journey and the achievement of taking down the richest city of the world at the time. Delhi suffered a great loss due to this and took a century to recover.

Timur started a war with Bayezid I, sultan of the Ottoman Empire, and the Mamluk sultan of Egypt Nasir-ad-Din Faraj. Bayezid began annexing the territory of Turkmen and Muslim rulers in Anatolia. As Timur claimed sovereignty over the Turkoman rulers, they took refuge behind him.

Kingdom of Georgia, a Christian kingdom dominanted on the most of Caucasus, was subjected many times by Timur between 1386 and 1403. These conflicts were intimately linked with the wars between Timur and Tokhtamysh, the last Khan of Golden Horde. Timur moved back to destroy the Georgian state once and for all. He demanded that George VII should hand over the Jalayirid Tahir but George VII refused and met Timur at the Sagim River in Lower Kartli, but suffered a defeat. After the war, of those who survived the fighting and reprisals, many thousands died of hunger and disease, and 60,000 survivors were enslaved and carried away by Timur's troops. He also sacked Sivas in Asia Minor.

Prior to attacking Syrian cities, Timur had initially sent an ambassador to Damascus who was executed by the city's Mamluk viceroy, Sudun. In 1400, he started a war with the Mamluk sultan of Egypt Nasir-ad-Din Faraj and invaded Mamluk Syria.

The Mamluks decided to fight an open battle outside the city walls. After two days of skirmishing, Timur's cavalry moved swiftly in arc shapes to attack the flanks of their enemy lines, while his center including elephants from India held firm. Fierce cavalry attacks forced the Mamluks led by Tamardash, governor of Aleppo, to break and flee towards the city gates. Afterwards, Timur took Aleppo, then he massacred many of the inhabitants, ordering the building of a tower of 20,000 skulls outside the city.

An army led by the Mamluk Sultan Nasir-ad-Din Faraj was defeated by Timur outside Damascus leaving the city at the mercy of the Mongol besiegers. With his army defeated, the Mamluk sultan dispatched a deputation from Cairo, including Ibn Khaldun, who negotiated with him, but after their withdrawal he put the city to sack. Timur's soldiers also committed mass rape against the women of Damascus and tortured the people of the city by burning them, using bastinados and crushing them in wine presses. Children died of starvation. Timur carried out these rapes and atrocities in Syria against his own Muslim co-religionists.

After the battle, Timur moved through western Anatolia to the Aegean coast, where he besieged and took the city of Smyrna, a stronghold of the Christian Knights Hospitalers. The battle was catastrophic for the Ottoman state, fracturing what remained and bringing almost total collapse of the empire. This resulted in a civil war among Bayezid's sons. The Ottoman civil war continued for another 11 years (1413) following the Battle of Ankara. The battle is also significant in Ottoman history as being the only time a Sultan was captured in person.

Timur preferred to fight his battles in the spring. However, he died en route during an uncharacteristic winter campaign. In December 1404, Timur began military campaigns against Ming China and detained a Ming envoy. He suffered illness while encamped on the farther side of the Syr Daria and died at Farab on 17 February 1405, before ever reaching the Chinese border. After his death the Ming envoys such as Fu An and the remaining entourage were released by his grandson Khalil Sultan.

The power of Timurids declined rapidly during the second half of the 15th century, largely due to the Timurid tradition of partitioning the empire. The Aq Qoyunlu conquered most of Iran from the Timurids, and by 1500, the divided and wartorn Timurid Empire had lost control of most of its territory, and in the following years was effectively pushed back on all fronts. Persia, the Caucasus, Mesopotamia, and Eastern Anatolia fell quickly to the Shiite Safavid Empire, secured by Shah Ismail I in the following decade. Much of the Central Asian lands was overrun by the Uzbeks of Muhammad Shaybani who conquered the key cities of Samarkand and Herat in 1505 and 1507, and who founded the Khanate of Bukhara. From Kabul, the Mughal Empire was established in 1526 by Babur, a descendant of Timur through his father and possibly a descendant of Genghis Khan through his mother. The dynasty he established is commonly known as the Mughal dynasty though it was directly inherited from the Timurids. By the 17th century, the Mughal Empire ruled most of India but eventually declined during the following century. The Timurid dynasty finally came to an end as the remaining nominal rule of the Mughals was abolished by the British Empire following the 1857 rebellion.