Rod Stewart was born and raised in London, England.
There’s no word on Stewart’s religion before he married Penny Lancaster, his third wife. Considering the musician’s alcohol and drug abuse, philandering, divorces, and children out of wedlock, chances are he wasn’t deeply committed to Christianity.
But now that Penny’s in his life, he’s a devoted member of the Church of Scotland, a Presbyterian church. Both of his children with his current wife were baptized at the couple’s church in Edinburgh, Scotland.
But it wasn’t just his wife that prompted Stewart to dedicate himself to his religion. After the September 11th terrorist attacks, Stewart turned to God. Lancaster explains,
After the tragedy we began going to church a lot. Wherever we were on tour, if there was a church and the door was open, we’d go in and have a prayer.
Stewart also makes references to Christianity in some of his lyrics, but it seems mostly to be in passing. Even his songs “Blind Prayer” and “Heaven” are more about women than anything of religious substance.
One of Stewart’s song shows off some of his political substance. He was onto the gay rights movement way before gay marriage was a cause célèbre. He also wrote a song about a hate crime titled, “The Killing of Georgie, Part I and Part II” released in 1976, tells the story of a gay man who was rejected by his family, found an accepting home in New York City, and was eventually killed by a gang. The narrator of the story, a friend of Georgie’s, doesn’t care that he’s gay and doesn’t understand why anyone else would. Sadly he stopped singing this song live years and years ago because he had a speaker fall on him while he was performing it. Reason being? He is very superstitious. 
Stewart says that there were a lot of gay people in his life at the time, and this song was based on the true story of a friend of his.
I think it was a brave step, but it wasn’t a risk. . . . But it was a subject that no one had approached before. And I think it still stands up today.
As far as an endorsement of a political party or candidate, you’re not going to get anything from Stewart. Based on his background and his participation in the gay rights movement early on, we can guess he’s pretty liberal. Unless, of course, being with his wife changed more than just his dedication to God.