The Supreme Court’s birthright-citizenship ruling was a 6-3 decision: Chief Justice John Roberts wrote the majority, joined by Justices Sonia Sotomayor, Elena Kagan, and Ketanji Brown Jackson, with Justice Brett Kavanaugh concurring separately on narrower statutory grounds.

How each justice voted

Justice| Vote
---|---
John Roberts| Majority, upheld birthright citizenship. 68
Sonia Sotomayor| Joined the majority. 68
Elena Kagan| Joined the majority. 68
Ketanji Brown Jackson| Joined the majority. 68
Brett Kavanaugh| Concurred separately, saying federal law also protected citizenship at birth. 68
Clarence Thomas| Dissented. 68
Neil Gorsuch| Dissented. 68
Samuel Alito| Dissented. 68
Amy Coney Barrett| The available reporting I found did not clearly specify her separate position in the snippet, though the ruling was described as a 6-3 decision with a separate concurrence and three dissents. 68

What that means

The practical result was that the Court rejected President Trump’s attempt to limit birthright citizenship, keeping the longstanding rule that children born in the United States are citizens.

One wrinkle: reporting described the case as “6-3” even though only five justices fully joined the Roberts opinion, because Kavanaugh agreed with the outcome on different grounds.

If you want, I can also lay this out as a simple “who joined whom” vote breakdown.