His great grandfather, Pandit Mani Ram, had a high rank at the Mughal Court in the reign of Shah Alam II.

His father, Rai Brahm Nath, also known as Rae Budh Singh, worked for a time for Mountstuart Elphinstone on a diplomatic mission to Peshawar (1808–1809).

[4] Alexander Burnes and Mohan Lal led an expedition to Central Asia in 1832–1834 for procuring political and military intelligence and became firm friends.

Later, Mohan Lal was the Commercial Agent for the British on the Indus and Political Assistant to Burnes in Kabul during the First Anglo-Afghan War.

Mohan Lal had learned Persian in Delhi and travelled in the garb of a Muslim, under the pseudonym of "Aga Hasan Jan"[8] or as "Mirza Quli Kashmiri" in Persia and Afghanistan collecting information vital for his British superiors.

[10] During his time in Europe he met Queen Victoria, Prince Albert and Frederick William IV of Prussia, the latter gifting Mohan Lal an inscribed ivory carving of himself.

The painting was exhibited by the Royal Scottish Academy in 1845 under the title "Mirza Mohun Lal, Persian secretary to the British Mission at Cabool, and who had previously accompanied Sir Alexander Burnes on his journey to Bokhara".

According to his biographer Hari Ram Gupta, Mohan Lal is reported to have written an extensive diary until his death, but by 1943 its location was no longer known.