Under the policy, anyone who breaches the upcoming UK quarantine rules and fails to self-isolate could be fined £1,000 or face potential prosecution.
Arrivals will be required to fill in a “contact locator form”, including details on where they will isolate and how they can be contacted.
Speaking at the daily Downing Street coronavirus briefing, the prime minister said the government would review the measures every three weeks and would "explore the possibility” of “travel corridors” with countries with low rates of coronavirus.
But the 14-day quarantine policy has come under fire from an increasing number of Tory backbenchers, including former prime minister, Theresa May.
Mr Johnson's predecessor joined a growing number of Tory voices expressing concern for at the plans, calling on ministers to ensure the country remains "open for business".
Addressing the House during Wednesday's Prime Minister's Questions, Mrs May said the 14-day quarantine would "close Britain off" and urged ministers to develop an "international aviation health screening" programme.
But Mr Johnson told the Downing Street briefing on Wednesday evening that it was the right time to introduce the policy in order to minimise the risk of "imported cases triggering a second peak".
He said: “Once community transmission was widespread within the UK, cases from abroad made up a tiny proportion of the total.
“At the same time you will remember international travel plummeted as countries around the world went into lockdown. As a result measures at the border were halted because they made little difference at the time in our fight against the virus.
“Now that we’re getting the virus under control in the UK, there is a risk that cases from abroad begin once again to make up a greater proportion of overall cases. We therefore need to take steps now to manage that risk of these imported cases triggering a second peak.”
Mr Johnson would not be drawn on whether Britons would be able to go abroad on holiday this year, but urged people to follow Foreign Office advice and "avoid non-essential travel.”