The Welsh Secretary sold the 17th-century terraced house in Amersham, Buckinghamshire, in November, for £320,000.
The property is situated about 500 yards from the route of the London to Birmingham section of HS2, which was given the green light last week by Transport Secretary Justine Greening.
Mrs Gillan has previously threatened to resign over HS2, which is bitterly opposed by many of her Chesham and Amersham constituents. But last week she said “good progress” had been made in mitigating the effects of the line with tunnels.
A spokesman for Mrs Gillan said her house had been on the market since June 2010 and was sold for 20 per cent under the original asking price.
She sold it because neither she nor her husband were able to use the stairs. Mrs Gillan has mobility problems after an illness in 2006 and her husband is 84.
“It had nothing whatsoever to do with HS2,” the spokesman said.
But Seb Berry, an independent councillor for the nearby town of Great Missenden, said: “We now have an MP who sits in the Cabinet that has approved a policy that will blight many homes in her own constituency – and yet she no longer owns a property here.
“That will make local people – many whom were in tears over the HS2 decision – very angry.”