Keir Starmer ruled out quitting the ECHR because it would jeopardise deportation deals and hinder the fight to restore control of Britain's borders.
The Prime Minister said countries would refuse to sign agreements with the UK "if in the next breath, you'll say you don't believe in international law".
But the Home Office has confirmed it will overhaul how Article 8 of the European Convention on Human Rights - is used in immigration cases.
Ministers will, later this year, bring forward new legislation to "clarify Article 8 rules and set out how they apply in different immigration routes so that fewer cases are treated as 'exceptional'".

Asked at a press conference - by the Daily Express - if going further on immigration would require "disentangling ourselves" from the ECHR, Sir Keir Starmer said: "No, I don't think that that is necessary.
"I also remind myself that the international agreements we've signed have given us the basis for the deals that we've struck on illegal migration.
"So the Home Secretary has moved fast, working with other countries to put in place materially improved deals with other countries in relation to migration that would not have been possible if we had been saying at the same time we're about to withdraw from our international obligations.
"You can't strike those deals with other countries to work more closely together on law enforcement, to smash the gangs and to work on returns agreements - which is what we want to do - if in the next breath, you'll say you don't believe in international law."
But he admitted "the right balance" needed to be made between individual rights and "the national interest".
"There's a balance set out in legislation already, that needs to be adjusted in my view," Sir Keir said.
The Home Office on Monday confirmed it will introduce new legislation to limit how Article 8 is being used in immigration cases.
The "public interest test" will be strengthened to "make it clear that Parliament needs to be able to control our borders".
And migrants trying to "get round the rules", for example by using Article 8 to apply to stay after travelling to the UK on a short-term visa, will likely lose their cases, under the new rules.
The Home Office believes the legislation - which will introduce a framework - will "limit successful claims" from individuals who "frustrate and delay removal with spurious claims in an attempt to stretch out their stay in the UK, and thereby increase the eventual likelihood of having an Article 8 claim upheld".
The majority of Channel migrants who make "immediate" claims for "wider family members" will also lose their cases.
Summarising the changes, the Home Office revealed in its long-awaited White Paper: "There have long been family rules and entitlements within the UK system for close family members to reunite across borders.
"There have also long been provisions which allow for exceptional circumstances which draw on Article 8 of the Human Rights Act and ECHR, which expresses the right to a family and private life.
"However, increasingly in recent years, the number of cases decided by the Home Office and the courts on the basis of 'exceptional circumstances' has substantially increased."
The Prime Minister, who said the country risks becoming an "island of strangers" without better integration, said he wanted net migration to have fallen "significantly" by the next general election - but refused to set a target number.
The plan, which includes changes to the way human rights laws are applied, is aimed at making the immigration system "controlled, selective and fair", Sir Keir said.
The Government's promise to "take back control of our borders" comes as Labour battles a surge in support for Reform UK, which won the Runcorn and Helsby by-election and council seats across England with policies including a "freeze" on immigration.
Net migration - the number of people arriving in the UK minus those leaving - stood at 728,000 in the year to mid-2024, down from the peak of 906,000 the previous year.
Measures in the highly-trailed White Paper also includes:
- Migrants will need to wait 10 years rather than five to apply for settlement or citizenship, although workers who significantly contribute to society, such as nurses, doctors and engineers, could be fast-tracked.
- A higher standard of English will be required across all immigration routes, including, for the first time, adult dependents required to display a basic understanding of the language.
- Stricter tests for colleges and universities offering places to foreign students and a reduction in the time graduates can remain in the UK after their studies from two years to 18 months.
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