This bronze is identified as Kalki, an avatar of Vishnu.  The vertical religious mark on the forehead (Namam) point to the Vaishnavite nature, the Conch on his left hand to Vishnu and the sword on his right hand is an attribute of Kalki.

This is the first Kalki in this form (standing two armed holding conch and sword) that I have come across. I got similar comments from my collector friends. Based on what we see in this bronze there does not seem to be any other explanation.  See the note at the bottom, dated 18 Aug 2018. Most of the depictions of Kalki, in paintings, show him riding a white horse holding a sword. Sometimes Kalki is depicted with a horse face.

Wearing crown and the usual set of ornaments, Kalki stands in Samapada, without any bend. The back is worked on with the same diligence as the front. Typical of South Indian bronzes. It is a two-piece construction, with the pedestal cast separately.

Kalki avatar is yet to happen. It is believed, as it was the case with earlier avatars, Kalki will appear at the time of need and reestablish purity, piety and virtue.

The casting is very fine. Notice the thickness of the top flat surface of the pedestal.

This bronze is from Tamil Nadu. It is about 7 cm in height. There is no noticeable ritual wear. The patina is deep and the bottom shows signs of use.  This bronze may date to the nineteenth century.

The casting quality and the subject matter makes it special.

18 Aug 2018: Found one example of Kalki with similar iconography. It is in Parthasarathy Temple, Chennai. As you enter the main Gopuram, there is a newish Mantap on your right. Some of the pillars in that Mantap have Vishnu’s avatars depicted on them. On one of the pillars near Yagya Shala, there is relief sculpture of Kalki with similar iconography.  Tempted as I was to take a quick photo, I had to remind myself few times photography is prohibited inside the temple.