He subsequently resigned his practice so that he could devote his time to the abolitionist movement, with which he first became involved in 1826, joining the Anti-Slavery Society in London in 1827.
Beldam's efforts at this period were mostly investigating abuses of the interim measures by which slaves would become apprenticed to their former masters as a means of allowing them to develop as fully independent, free citizens.
Thanks to Beldam's careful collection of information, Parliament was forced to end the apprenticeship system in 1838, three years early.
After this final liberation of slaves in the British colonies, Beldam became involved in international efforts to end slavery everywhere.
A modest man, he refused two appointments he was offered by the Colonial Office, made no attempt to enter politics and generally maintained a low profile in the movement.