MP Stephen Hammond’s researcher is hoping to take centre stage as he bids for election as a member of parliament.
In the Wimbledon constituency, Mr Hammond will stand against Labour councillor Andrew Judge, who represents Abbey ward and ran for MP in 2010.
They will go up against Liberal Democrat candidate Shas Sheehan.
Mr Holmes, 25, who was selected on Tuesday, August 12, said: "I have been involved in the Conservative party for nine or ten years and I am an ex-local councillor in Southampton where I went to university.
"I have worked a lot in Merton with Stephen Hammond and I know a lot of the issues and key players at the council."
Mr Holmes, who lives in Clapham, said Mr Hammond had given him some advice on being an MP.
Mr Hammond, who is the former parliamentary under secretary of state for transport, said: "It’s been an honour representing Wimbledon for the past ten years and I'd be even more honoured to be elected again in 2015.
"The Conservatives have delivered for Wimbledon. One of my key pledges was continued investment in our transport, hospitals and schools.
"We've done just that. I want the opportunity to continue to work hard and deliver for my constituents."
Ms McDonagh has been the MP for Mitcham and Morden since 1997. She said: "I’m born and bred in Mitcham and Morden, and have lived here my entire life.
MP Siobhain McDonagh
"I’d like to welcome my opponents to the area - it’s a great community, and one I’m proud to represent.
"We’ve achieved big strides together during my time as an MP.
“However, the progress we’ve made on things like getting bigger community police teams and money to rebuild St Helier is being reversed by the current government, so if I’m re-elected my job will be to do all I can to make Mitcham and Morden better again."
A statement from the Merton Labour group on behalf of Coun Judge said: "Andrew is an extremely well regarded and highly experienced councillor, with nearly 20 years experience on Merton Council.
Councillor Andrew Judge
“He led the council between 2001 and 2006, and since 2010 he has looked after planning and regeneration on the Cabinet.
“He has represented Abbey ward in Wimbledon since 2010, and his tireless work in the ward between 2010 and 2014 was instrumental to Labour's success in gaining all three seats in May.
"Andrew's professional background as a criminal barrister and his extensive experience in local government make him incredibly well qualified to stand as an MP.
“Everyone in Wimbledon will be doing all they can to help him between now and next May."
The Liberal Democrats have put forward Mrs Sheehan, a former councillor in Richmond.
Mrs Sheehan stood for the Wimbledon seat in 2010 and will be standing for the same seat again next year.
Mrs Sheehan said: "I will be working very hard on St Helier Hospital and improving mental health services in the borough.
"I want to bring back the Freedom pass."
Working as head of office for MP Susan Kramer gave former housewife Mrs Sheehan an insight into the powers an MP has.
Parliamentary elections will take place on Thursday, May 7, 2015.