Maharaja Jaswant Singh (26 December 1629 – 28 December 1678) was the ruler of Marwar in the present day Indian state of Rajasthan. He was the Rajput belonging to the Rathore Clan. His father was Maharaja Gaj Singh.
Jaswant Singh succeeded his father on his death by special decree of the Emperor Shah Jahan, in accordance with his father's wishes, on 6 May 1638.
He was installed on the gaddi at Sringar Chowki, Mehrangarh, Jodhpur, on 25 May 1638. He was granted the personal title of Maharaja by the Emperor Shah Jahan, on 6 January 1654.
In the Battle of Dharmatpur, Jaswant Singh opposed Aurangzeb. The battle was fought on 15 April 1658, fifteen miles from Ujjain. Jaswant could have attacked Aurangzeb but he allowed Murad's armies to join Aurangzeb. He was desirous of beating both mughal princes at once. This delay allowed Aurangzeb to win over the mughal general, Kasim Khan, who was sent by Shah Jahan to help Jaswant. Kasim Khan defected as soon as the war started but 30,000 Rathores of Jaswant decided that they would not leave the field. Some prominent generals in Maharaja's army were Mukund Singh Hara of Kotah and Bundi, Dayal Das Jhala, Arjun Gaur of Rajgarh in Ajmer province and Ratan Singh Rathore of Ratlam. Jaswant attacked both Aurangzeb and Murad and they barely escaped.
Finally the unequal contest ended and Aurangzeb named the place of victory Fatehabad. In this battle Durga Das Rathore changed four horses and lost about half a dozen swords (they broke due to intense fighting) and he finally fell down half dead. Maharajah ordered him to be carried away.
Prithviraj Singh was Jaswant Singh's son. It is chronicled in Marwar khyats that Aurangzeb presented Prithviraj Singh a dress which was poisoned. On wearing this dress Prithviraji died in great pain at Delhi, 8 May 1667. Prithviraj was a good leader and a brave prince. Jaswant could not get over the shock of his son's death.
Maharaja Jaswant died at Jamrud, near Peshawar, on 28 December 1678. At the time of his death two of his wives were pregnant, and both would later bear sons. This led to a war in which there were attempts to install Jaswant Singh's elder surviving son Ajit Singh Rathore as ruler of Marwar.