The procession, which included floats, pipe bands and dancers, set off at 12:00 GMT in the Digbeth area of the city.
Last year, more than 80,000 people turned out to celebrate the occasion.
The parade, which has passed through Digbeth since 1996, is regarded as the third largest in the world after those in New York and Dublin.
This year's celebrations have been taking place on the actual date of St Patrick's Day and have the theme of The Gathering, which organisers say is about encouraging people of Irish descent to visit the county, town and or village of their ancestry.
Pat Murphy-Wright, cultural development officer for the charity Irish in Birmingham, said: "The parade is about people embracing their roots and helps to teach children at local schools about their cultural background."
John Lines, the Lord Mayor of Birmingham, told BBC News the celebrations were going really well.
He said: "The weather looks fine and everyone's smiling. Such wonderful costumes - people must have spent all year preparing for this.
"Aren't we lucky in Birmingham?"
Tens of thousands of people have lined the streets of Birmingham for the annual St Patrick's day parade.