Albert Barnes Commentary Acts 26:10

"And this I also did in Jerusalem: and I both shut up many of the saints in prisons, having received authority from the chief priests, and when they were put to death I gave my vote against them." — Acts 26:10 (ASV)

Which thing I also did. See Acts 8:3.

And many of the saints. Meaning, many Christians (Acts 8:3).

And when they were put to death. In the history of those transactions, there is no account of any Christian being put to death, except Stephen (Acts 7). But there is no improbability in supposing that the same thing that had happened to Stephen had occurred in other cases. Stephen was the first martyr, and as he was a prominent man, his case is particularly recorded.

I gave my voice. Paul was not a member of the Sanhedrin, and this does not mean that he voted, but simply that he joined in the persecution; he approved it; he consented to the saints being put to death . The Syriac renders it, "I joined with those who condemned them." It is also evident that Paul instigated them in this persecution and urged them on to deeds of blood and cruelty.