Holding independent charge, the 34-year-old Lad was minister for infrastructure development, information and broadcasting and Kannada and culture.
"Though there was no pressure from the CM or my party, I have resigned because I don't want my party (Congress) to be embarrassed further. I am open to investigations and am sure I will be proved innocent after the investigations," Lad asserted.
Lad is the first minister to quit over 6 months after the Congress returned to power following its victory in the state legislative assembly elections in May.
The resignation comes ahead of the winter session of the state legislature from Nov 25 at Belgaum in the northern region of the state, amid mounting pressure from the opposition parties - the Bharatiya Janata Party, the Janata Dal-Secular and the Karnataka Janata Party, headed by former chief minister BS Yeddyurappa.