The proposals follow the Government giving powers to authorities to abolish generous tax breaks for holiday homes and owners of property standing idle.
Devon and Cornwall boast around 26,000 second homes and have among the highest levels of second-home ownership, which critics blame for pushing up house prices beyond the reach of local people.
Earlier this year, the Western Morning News revealed tax breaks on second homes and empty properties in the Westcountry cost the region £25 million annually.
There are estimated to be 26,000 second homes in Cornwall and Devon, and critics blame the high proportion of holiday homes for pricing local people out of the market and putting schools, shops and pubs at risk.
The discount ranges from 10% to 50%, depending on the council. Cornwall Council's is 10%. MPs say any extra cash will not solve the housing crisis in the region, but the money can be used to underwrite affordable community housing and shore-up services.
Councillor Jeremy Rowe, leader of the Liberal Democrat group on Cornwall Council, said: "The second home council tax discount is an anathema which harms local services.
"I'm delighted that the Lib Dems in government have made the change that allows councils to charge full council tax on second homes and equally delighted that Cornwall is proposing to implement the change at the first opportunity."
Government figures show the estimated cost of the second-home discount is £2.2 million in Devon and £2.1 million in Cornwall. It costs a further £1 million in parts of Somerset and Dorset.
On top of that, the relief afforded to empty properties in the Westcountry stands at almost £20 million.
Mr Rowe added: "The authority is also proposing that empty homes will be exempt from council tax only for the first month.
"This change is aimed at encouraging owners not to leave homes empty when there are more than 25,000 families on the housing waiting list.
"Indeed, the council is going further and proposing a penalty premium of an extra 50% on empty properties left vacant for more than two years.
"The council has a number of grant programmes in place to help the owners of empty properties bring them back into use, so there should be no excuse.
"In addition a loophole that allowed homeowners to escape council tax if they could show that a house was undergoing major repairs is being closed and these will only get a 50% discount for a single year and then have to pay full council tax thereafter."
