Jack Lopresti said a letter sent to party members calling for a new candidate was part of an "attempt to destroy my character and reputation".
The Filton and Bradley Stoke MP left his wife for fellow MP Andrea Jenkyns, who gave birth to their son in March.
Mr Lopresti was reselected at a meeting on Friday evening.
An anonymous letter sent to Conservative Party members in the constituency earlier this month said there were "many of us who feel very strongly that Mr Lopresti is not representing our constituency in a very good way".
It added there were "several excellent people" who should be given the chance to become the prospective parliamentary candidate.
The local party has reacted to the letter by writing to party members assuring that "appropriate legal action" would be taken if the writer was identified.
He was first elected in 2010 and re-elected with a near-10,000 majority five years later.
In November last year, it was reported he had become engaged to Ms Jenkyns â€” who ousted former Labour shadow chancellor Ed Balls to become MP for Morley and Outwood in 2015. Their son, Clifford George, was born in March.
"For the last month my family and I have been subject to a vicious smear campaign with racist overtones," he said.
"Since the day after my son Clifford was born, my office has been bombarded with bogus calls from people purporting to be national journalists and with dark threats of illegally taped conversations. This has deeply upset my staff.
"I have had many messages of support from party members and lots of constituents, and I am sure that this recent attempt to destroy my character and reputation has been orchestrated by a small handful of people.
"I can only think that this is as a result of personal choices I have made in my private life, which some may not have approved.
"I love my fiancee Andrea and am extremely proud of my young son Clifford and nobody will ever be able to change that."

Legally, it needs at least 5% of local electors for a referendum to go ahead.
Those behind the petition say a mayor would offer more dynamic leadership and "rise above party politics".
Council leader Tim Warren said it felt "unnecessary" so soon after the elections. If successful, a directly elected mayor would replace him.
The council announced on Monday that it had received 6,818 valid signatures. A further 2,789 signatures were ruled to be invalid.
Directly elected mayors were created by the Local Government Act 2000 as one option for local government, as long as the idea was backed in a referendum.
Bath & North East Somerset Council said the threshold set out under the 2000 Act had been reached and "it is anticipated that the referendum will be held early next year".
In Bath, the council is run by a leader and cabinet system.
Philip Raby, one of the team working for a referendum, said they favoured holding it on 5 May 2016, the day of the police and crime commissioner elections.
He felt a directly elected mayor would offer "visible and accountable leadership" for the wider area - something he felt the current system did not offer.
Mr Warren said there were "challenging budgetary issues" to concentrate on and questioned whether there was much public appetite for a referendum.
Local petitions sparked referendums which resulted in elected mayors in Salford, Greater Manchester in 2012 and in Copeland, Cumbria in 2015.
The Localism Act 2011 allowed central government to trigger referendums for elected mayors - but of the ten held in May 2012, only Bristol voted in favour of getting a mayor.
A Conservative MP who faced deselection by his own party has blamed a "vicious smear campaign" against him following revelations about his private life.
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A referendum on an elected mayor for Bath and North East Somerset will be held in 2016, after a petition reached the threshold of 6,437 votes.