The two had an affair while studying at college but the woman's parents had objected to the relationship and asked her to stop seeing the accused, they said.
The man, who had left for Coimbatore in search of a job some months ago, returned to Mallapuram village after hearing that the woman's parents were planning to marry her.
He followed the family when they were purchasing the marriage items yesterday and confronted her at the bus-stand, demanding that she accept his proposal.
When she refused, he attacked her with a sickle.
The man has been arrested and remanded in judicial custody, police said.