Iain Murray describes him as an evangelical Arminian in his Lloyd-Jones biography. Morgan was pastor of Westminster Chapel, London in the 1900's and 1910's and again in the thirties. He was an evangelical leader who was probably mainly known as an expositor who advocated for the authority of the Bible against liberalism and modernism and apparently it was Lloyd-Jones stance on those issues and his powerful preaching that led Morgan to bring him to Westminster Chapel. Other than that, I don't know that much about him.
Here are some pages with biographical material that I turned up: