He received his education at the University of Munich, where he was a student of Karl Friedrich Schimper (1803–1867). Afterwards he served as a private secretary to a Silesian nobleman, and during his spare time performed studies of cryptogramic flora of the Sudetenland.
In 1841 he was appointed curator of the Leuchtenbergsche Naturalienkabinett in Eichstätt. Two years later he accompanied Mutius von Tommasini (1794–1879) on a botanical excursion through Istria and Tyrol, and in 1847 conducted botanical research in Bosnia. During this time period he also performed phytogeographical studies in southern Bavaria. In 1854 he became an associate professor, and in 1857 was appointed to the second chair of botany, as well as first curator of the herbarium at the University of Munich.
Sendtner was a pioneer in the field of phytogeography, and in his research conducted important analyses involving the vertical distribution patterns of different types of vegetation. The genus Sendtnera Endl. (1840) is probably named after him, although no etymology is given. As a taxonomist he described many plants within the family Solanaceae.
- Die Vegetationsverhältnisse Südbayerns nach den Grundsätzen der Pflanzengeographie und mit Bezugnahme auf die Landeskultur (Vegetation conditions of southern Bavaria in accordance with principles of plant geography and with reference to the local culture), 1854
- Die Vegetationsverhältnisse des Bayerischen Waldes nach den Grundsätzen der Pflanzengeographie (Vegetation conditions of the Bavarian Forest in accordance with the principles of plant geography), 1860