The former prime minister has published a 52-page report of his actions ahead of a grilling by MPs on Wednesday.
In it, he says his assurances to MPs that lockdown rules had been followed were made in “good faith”.
Mr Johnson faces being suspended or even expelled from Parliament, if MPs decide he deliberately misled them.
A group representing families of Covid victims said his claim to have acted in good faith was “sickening”, and it was “obvious” he deliberately misled MPs.
Since April last year, the Commons Privileges Committee has been investigating whether Mr Johnson initially misled Parliament over what he knew about parties in No 10 during lockdown.
After media stories about what would become known as the Partygate scandal emerged in late 2021, Mr Johnson denied to MPs that Covid rules banning socialising indoors had been broken.
But an inquiry by senior official Sue Gray later found rule-breaking had taken place across multiple events, and police issued fines to 83 people, including Mr Johnson himself, for breaching Covid laws.
The committee, chaired by veteran Labour MP Harriet Harman, but with a Tory majority, has previously said Mr Johnson may have misled Parliament on multiple occasions, and evidence suggests rule breaches would have been “obvious” to him at the time.
In his defence document, prepared by his taxpayer-funded legal team, headed by top barrister Lord Pannick KC, Mr Johnson says he had not “intentionally or recklessly” misled MPs, and would “never have dreamed of doing so”.
He said he believed at the time that events he attended in No 10, including to bid farewell to departing staff, abided by restrictions because they were “essential for work purposes”.
He added that it “remains unclear to me” why he was fined for attending a gathering in No 10 for his birthday in June 2020.
Mr Johnson said he relied on officials to advise him about other events in the building he did not attend, and they did not tell him rules were broken.
“I believed – and I still believe – that this was the earliest opportunity at which I could make the necessary correction,” he added.
“It was not fair or appropriate to give a half-baked account, before the facts had been fully and properly established.”
The committee is expected to publish its verdict on Mr Johnson by the summer.
It has assembled evidence including written statements from 23 witnesses, official diaries, emails between officials, and WhatsApp messages handed over by the former prime minister’s legal team.
Dominic Cummings row
It will publish a “core bundle” of documents on Wednesday morning, ahead of Mr Johnson’s hearing later in the day.
In his defence document, Mr Johnson claimed the committee had not found evidence he intentionally misled MPs.
He said the “only exception” were assertions made by his former top aide Dominic Cummings, whom he said was “discredited” and was motivated by personal animosity.
Mr Cummings hit back on Twitter, saying a drinks party in the No 10 garden attended by Mr Johnson had been deemed to have broken the rules by police, with officials fined for attending.
In an interim report published earlier this month, the committee said Mr Johnson’s statements to MPs, as well as his performance at Covid press conferences, show that he understood what the rules were.
In a statement on Tuesday, the committee said Mr Johnson’s written submission contained “no new documentary evidence”.
In his document, Mr Johnson attacked the conduct of the inquiry, accusing the committee of being “highly partisan” and going against precedents set by previous similar inquiries.
The committee has decided that whether he intended to mislead MPs is not relevant to what it has been charged with investigating: whether it was stopped from doing its job by his statements to MPs.
But if they find that it was, then his intentions will be considered when deciding any punishment they recommend.
A finding that he deliberately misled MPs is likely to attract the strongest sanction. Another option is they conclude he misled Parliament “recklessly”.
In his submission, the former prime minister hit out at this reasoning, saying the idea of misleading MPs recklessly was an “entirely novel concept”.
The full House of Commons will have to approve the committee’s final recommendations, as well as any sanctions. Conservative MPs will be given a free vote, meaning they will not be told how to vote by party managers.
The possible punishments range from ordering him to apologise to suspending him from the Commons.
If he is suspended for more than 10 days, this could trigger a by-election in his constituency – although suspensions of this length have been rare in the past.