Born in Breddin, Germany, Mielatz was both an etcher and teacher. He received his early art training at the Chicago School of Design. He began to etch in 1883 and exhibited for the first time at the New York Etching Club in 1884. He endlessly experimented in all aspects of the intaglio media. Mielatz was elected an Associate in the National Academy of Design and succeeded James Smillie as instructor in etching at the Academy serving in that position for 15 years.

He was the first major American artist to portray the beauty and excitement of New York City on the copper plate. His etchings particularly of wet street surfaces proved to be an influence on the later work of Martin Lewis.