Martin Kastler (born 1974 in Nuremberg) was a German politician of the Christian Social Union of Bavaria (CSU) who was a Member of the European Parliament from 2003 until 2004 and from 2009 until 2014.

Kastler's first term in European Parliament for the CSU spanned 2003 to 2004, as successor of Emilia Müller, who was called to government by the former minister-president of Bavaria, Edmund Stoiber.

The Foreign Minister of the Czech Republic, Jan Lipavský, awarded Martin Kastler the medal in 2023 for his long-standing commitment and services to German-Czech, in particular Bavarian-Czech understanding for Diplomacy.Czech Foreign Minister awards medals for merits in diplomacy, on deutsch.radio.cz< /ref> Kastler is an initiator of the First European Citizens' Initiative whose aim is to protect Sundays as a day of rest Europe-wide.

Kastler believes that Sunday needs to be protected as a work-free day of family and rest in order that children do not run the risk of suffering from today's flexibilisation of the business world.

He hints at the historical entrenchment of the work-free Sunday in the European social welfare net as well as at the proven advantages of a free weekday on health.