Taking advantage of the change in sovereigns, Jai Singh's commander in the Deccan, Khan Jahan Lodi, rebelled with his Afghan followers.

[3] The following year, Jai Singh served in the expedition against the Sultanate of Bijapur under Asaf Jahan but their campaign was thwarted by the Deccan famine of 1630–1632.

Jadunath Sarkar states that Jai Singh captured "8,000 oxen loaded with provisions, arms, and rockets, besides 3,000 men" from the enemy.

[4][5] In 1636 Shah Jahan organized a grand campaign against the Deccan sultanates in which Jai Singh played a leading part, serving as the leader of the Rajput vanguard in the invasion of Bijapur.

For his part in these successful ventures Jai Singh was promoted to the rank of five-hazari and given equal number of troops under his control and the Chatsu district in Ajmer was added to his kingdom.

By defeating the Meo robber tribes in the north of Amber, Jai Singh further increased the size of his ancestral kingdom.

In the ensuing Mughal-Safavid War the Mughals twice attempted to eject the Persians from Kandahar under the command of Prince Aurangzeb (in 1649 and 1652) —on both occasions Jai Singh was present as an army commander, but the attempts failed due to the lack of adequate artillery and poor marksmanship of the Mughal gunners.

[8] A third grand attempt was made in 1653 under the command of Shah Jahan's oldest and favorite son Dara Shikoh, a rival of Aurangzeb, and again Jai Singh was sent with this army.

Shah Shuja in Bengal and Murad in Gujarat crowned themselves emperors, but Aurangzeb cleverly declared his intention of merely rescuing his father for the sake of Islam.

In the face of these triple dangers, Dara Shikoh now remembered Jai Singh—and the Rajput chief was made commander of 6000 and sent east along with Dara's son Sulaiman Shikoh and the Afghan general Diler Khan[11] They triumphed over Shah Shuja at the Battle of Bahadurpur (24 February 1658)[12] and chased him back to Bengal (May).

[13] Despite his victories Aurangzeb did not have a secure footing on the Mughal throne, still needing the support of the leading Muslim and Rajput generals.

Shivaji is noted to have said when receiving Jai Singh "I have come as a guilty slave to seek forgiveness, and it is for you to pardon or kill me at your pleasure."

However, the scorched earth of the defenders exhausted Jai Singh's food supplies and forced him to begin his retreat in January 1666.