When mercury placed in third house of horoscope the native is an intelligent person and earns through writings, poetry and editing works. The person is very hard working, conversant and luxuriant but less brothers or sisters, has many children and may a palmist and expert of Samudrik Shastra. As this house is owned by mercury so mercury in third house is always beneficial for writers, editors, speakers and astrologers.
Normally malefic planets give good results in third house of horoscope but mercury is a nature adopting planet so it becomes malefic with malefic and beneficial with beneficial. We cannot define mercury as 100% malefic or benefice planet. Most of the time mercury is found with planet sun but sometimes alone.
If mercury placed in third house in Cancer sign or Pisces sign the person will be justice lover, has a floating mind and coward too. If mercury sitting with mars in third house, the person has good relations with neighbour and mostly live far from home due to career and job. If mercury is in Gemini, Libra or Aquarius, native will be a Tantrik, Astrologer and he will have some secret knowledge of Tantra and Mantra. The person will gain fame and prosperity in this field and get a high position.
In Cancer, Virgo or Sagittarius lagna when Venus sitting in second house and mercury in third house, the person will do accurate predictions being an astrologer. He will have a sharp memory if mercury in third house aspected by good planets like Jupiter. He/she also gets fame and name as a good writer. So if you are having mercury in third house of horoscope, you can get similar results but will depend on the position and conjunction with other planets and may change some results accordingly.
Astrologer Sunil Kumar