Boris Johnson is set to take a starring role in Westminster politics once more after being selected as the Conservative candidate for Uxbridge and South Ruislip on Friday night.

The mayor of London, who was MP for Henley for seven years until being elected to City Hall in 2008, defeated three others on the shortlist following a secret ballot of party members in the constituency.

Johnson is attempting to return to the House of Commons ahead of a possible leadership contest that is expected to take place if David Cameron loses the general election next year.

About 100 local Conservative party members chose Johnson as their candidate after a hustings behind closed doors at Ruislip High School. He was cheered by a small number of onlookers as he arrived shortly before 7pm.

After the vote took place, Johnson said the members of the local association had "done him the honour" of selecting him to contest the election in "236 days".

He denied that this was the start of a campaign to enter Downing Street and was instead the beginning of a battle to retain the west London seat, which has a Tory majority of more than 11,000, for the Conservatives and stopping Labour from winning the next election. "This is act one, scene one of a very long process," Johnson said.

Asked whether he could be an MP while remaining mayor, he said "it had been done before" and there was no reason why it could not be done again.

Johnson sidestepped questions about whether he had broken a promise not to combine the two jobs. His mayoral term does not end until 2016.

Johnson decided to "whack in" his application to become the MP for the constituency after the long-serving Sir John Randall announced his retirement earlier this year, ending months of speculation about his political ambitions.

The prime minister has insisted that Johnson would be an electoral asset, but did not appear to have been given prior warning of his former Etonian schoolmate's decision to throw his hat into the Westminster ring.

Johnson defeated two local politicians, deputy leader of Hillingdon council David Simmonds, and Simon Dudley, deputy leader of Windsor and Maidenhead council, as well as Harrow-born barrister Suella Fernandes.

Johnson, 50, said the selection process had been "very enjoyable" and paid tribute to his three unsuccessful opponents.

His long-running campaign for a new airport in the Thames estuary at the expense of Heathrow, which employs more than 100,000 people in the area, did not deter party members from voting for Johnson.

After announcing his decision to seek selection for the Uxbridge seat, he used his column in the Telegraph earlier this month to claim that Heathrow could be kept open as a secondary airport.

Wayne Bridges, chairman of the Hillingdon and South Ruislip Conservative association, said that Heathrow was one of the issues that members had asked Johnson about, along with the proposed route of High Speed 2 – which is opposed by some local residents – and housing. "He was given quite a grilling, as were all the candidates," he said.

Johnson said he would consider buying a property in the constituency, according to Bridges, and that the issue of the party leadership did not come up in the session.