Natural law, and by extension natural rights were used to justify the secession of the American colonies from tyrannical British rule.
One of the most well-known examples of this thinking can be found in The Declaration of Independence:
"The unanimous Declaration of the thirteen united States of America, When in the Course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with another, and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation."
As you can see, Thomas Jefferson (the author) started this declaration by invoking the righteousness of natural law. He then added his own version of John Locke's words:
"The state of nature has a law of nature to govern it, which obliges every one: and reason, which is that law, teaches all mankind, who will but consult it, that being all equal and independent, no one ought to harm another in his life, health, liberty, or possessions… (and) when his own preservation comes not in competition, ought he, as much as he can, to preserve the rest of mankind, and may not, unless it be to do justice on an offender, take away, or impair the life, or what tends to the preservation of the life, the liberty, health, limb, or goods of another."
Jefferson used this thinking when composing the next paragraph:
"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. — That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, — That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness."
As you can see, Jefferson is using natural law to justify rebellion against the crown. At the same time, he is stating that the purpose of government being created by men was to protect rights. The Declaration of Independence was to give notice to King George III that the colonists were withdrawing their consent to be governed by him and his parliament.
The declaration continues with a very long list of grievances that justify rebellion. I will have a link below so you can read a full transcript of the document if you wish to read them.
After all of this justification being made Jefferson finally gets to the actual declaration itself:
"We, therefore, the Representatives of the united States of America, in General Congress, Assembled, appealing to the Supreme Judge of the world for the rectitude of our intentions, do, in the Name, and by Authority of the good People of these Colonies, solemnly publish and declare, That these United Colonies are, and of Right ought to be Free and Independent States; that they are Absolved from all Allegiance to the British Crown, and that all political connection between them and the State of Great Britain, is and ought to be totally dissolved; and that as Free and Independent States, they have full Power to levy War, conclude Peace, contract Alliances, establish Commerce, and to do all other Acts and Things which Independent States may of right do. And for the support of this Declaration, with a firm reliance on the protection of divine Providence, we mutually pledge to each other our Lives, our Fortunes and our sacred Honor."
As you can see, Jefferson is asserting the people themselves are the ultimate authority, and you can see that idea echoed in the preamble of The Constitution:
"We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America."
The rebellion and subsequent federation of states both relied on the principles of natural law for justification. Jefferson was unwavering in these principles, and I think this final quote from him will leave no doubt:
"our legislators are not sufficiently apprised of the rightful limits of their powers: that their true office is to declare and enforce only our natural rights and duties, & to take none of them from us. No man has a natural right to commit aggression on the equal rights of another; and this is all from which the laws ought to restrain him: and every man is under the natural duty of contributing to the necessities of the society; and this is all the laws should enforce on him: and, no man having a natural right to be the judge between himself and another, it is his natural duty to submit to the umpirage of an impartial third. the l when the laws have declared and enforced all this, they have fulfilled their functions, and the idea is quite unfounded that on entering into society we give up any natural right. the trial of every law by one of these texts would lessen much the labors of our legislators, & lighten equally our municipal codes."
-Extract from Thomas Jefferson to Francis W. Gilmer,
An overview of Natural Law: