Since 2001 he has been an editor of the Respekt weekly. Petr Třešňák focuses mainly on social and health issues. He is the co-founder and chairman of Naděje pro děti úplňku, an organisation that brings together parents of children with autism spectrum disorders and strives for better and more accessible social services for people with disabilities. In 2014, he won the Journalist Award of the Czech Psychiatric Society for his article "Children of the Full Moon" about children with autism and in the same year he received the Ferdinand Peroutka Prize. The book Zvuky probouzení (Waking Sounds) in which Petr Třešňák and his wife chronicle their experience of raising a daughter with autism, was nominated for the Magnesia Literary Prize in 2021.