Farid Khan started his Service under Bahar Khan Lohani, the Mughal Governor of Bihar. Because of his valour, Bahar Khan rewarded him the title Sher Khan (Lion Lord). After the death of Bahar Khan, Sher Khan became the regent ruler of the minor Sultan, Jalal Khan. Later sensing the growth of Sher Shah's power in Bihar, Jalal sought the assistance of Ghiyasuddin Mahmud Shah, the independent Sultan of Bengal. Ghiyasuddin sent an army under General Ibrahim Khan. But, Sher Khan defeated the force at the battle of Surajgarh in 1534 after forming an alliance with Ujjainiya Rajputs and other local chiefdoms. Thus he achieved complete control of Bihar.

After the death of Bahadur Shah of Gujarat in 1537, Qadir Shah became the new ruler of Malwa Sultanate. He then turned for support towards the Rajput and Muslim noblemen of the Khilji rule of Malwa. Bhupat Rai and Puran Mal, sons of Raja Silhadi accepted Service under the regime of Malwa in recognition of their interest in the Raisen region. By 1540, Bhupat Rai had died and Puran Mal had become the dominant force in eastern Malwa. In 1542, Sher Shah conquered Malwa without a fight and Qadir Shah fled to Gujarat. He then appointed Shuja'at Khan as the governor of Malwa who reorganised the administration and made Sarangpur the seat of Malwa's government. Sher Shah then ordered Puran Mal to be brought before him. Puran Mal agreed to accept his lordship and left his brother Chaturbhuj under Sher Shah's Service. In exchange Sher Shah vowed to safeguard Puran Mal and his land. The Muslim women of Chanderi, which Sher Shah took under his rule, came to him and accused Puran Mal of killing their husbands and enslaving their daughters. They threatened to accuse the Sultan on the Day of Resurrection if he did not avenge them. Upon reminding them of his vow for Puran Mal's safety, they told him to consult his ulema. The ulema issued a fatwa declaring that Puran Mal deserved death for this act. Sher Shah's troops then surrounded Puran Mal's fortress at Raisen. Upon seeing this, Puran Mal beheaded his wife and ordered the Rajputs to kill their families as he might have thought that personal honor was involved because of his lord going back on his promise. After this, the Rajputs then went into battle and all of them were killed by Sher Shah's troops. `Abd al-Qadir Bada'uni puts the number of Rajputs to 10,000 while Nizamuddin Ahmad puts it to 4,000.

It is clear from coins dated AH 945 (1538 AD) that Sher Khan had assumed the royal title of Farid al-Din Sher Shah & had coins struck in his own name even before the battle of Chausa

In 1538, Sher Khan attacked Bengal and defeated Ghiyashuddin Shah. But he could not capture the kingdom because of the sudden expedition of Emperor Humayun. On 26 June 1539, Sher Khan faced Humayun in the Battle of Chausa and defeated him. Assuming the title Farīd al-Dīn Shēr Shah, he defeated Humayun once again at Kannauj in May 1540 and forced him out of India.

Sher Shah built monuments including Rohtas Fort (now a UNESCO World Heritage Site in Pakistan), many structures in the Rohtasgarh Fort in Bihar, Sher Shah Suri Masjid, in Patna, built in 1540–1545 to commemorate his reign. He built a new city Bhera of Pakistan in 1545 and inside the city built historical grand Sher Shah Suri Masjid.}

Qila-i-Kuhna mosque, built by Sher Shah in 1541, at Purana Qila, Delhi, a Humayun citadel started in 1533, and later extended by him, along with the construction of Sher Mandal, an octagonal building inside the Purana Qila complex, which later served as the library of Humayun.

In 1543, Sher Shah Suri with a huge force of 80,000 cavalry set out against Maldeo Rathore (a Rajput king of Marwar). Maldeo Rathore with an army of 50,000 cavalry advanced to face Sher Shah's army. Instead of marching to the enemy's capital Sher Shah halted in the village of Sammel in the pargana of Jaitaran, ninety kilometers east of Jodhpur. After one month, Sher Shah's position became critical owing to the difficulties of food supplies for his huge army. To resolve this situation, Sher Shah resorted to a cunning ploy. One evening, he dropped forged letters near the Maldeo's camp in such a way that they were sure to be intercepted. These letters indicated, falsely, that some of Maldeo's army commanders were promising assistance to Sher Shah. This caused great consternation to Maldeo, who immediately (and wrongly) suspected his commanders of disloyalty. Maldeo left for Jodhpur with his own men, abandoning his commanders to their fate.

After this victory, Sher Shah's general Khawas Khan Marwat took possession of Jodhpur and occupied the territory of Marwar from Ajmer to Mount Abu in 1544.

Sher Shah was killed on 22 May 1545 during the siege of the Kalinjar fort of Rajputs. When all tactics to subdue this fort failed, Sher Shah ordered the walls of the fort to be blown up with gunpowder, but he himself was seriously wounded as a result of the explosion of a mine. He was succeeded by his son, Jalal Khan, who took the title of Islam Shah Suri. His mausoleum, the Sher Shah Suri Tomb (122 ft high), stands in the middle of an artificial lake at Sasaram, a town on the Grand Trunk Road.

Tarikh-i-Sher Shahi (History of Sher Shah), written by Abbas Khan Sarwani, a waqia-navis under later Mughal Emperor, Akbar around 1580, provides a detailed documentation about Sher Shah's administration.