1)Before Knowing effect of Mercury In 10th house we have to know about Mercury and 10th house. So you may read this
Prince Of Planet–Mercury
Tenth House–Profession House Of Your Horoscop—
2)Mercury In 10th house don’t consider so good regarding profession. The basic cause is Mercury is lord of 6th house and 3rd house Of Kalpurush chart and it is placed in the 10th house Of Karam. So the Genral impact is traboule in profession(due to 6th house lord impact) and struggle and doing own efforts(Due to 3rd house lordship impact) means don’t got a smooth success. But this is only one side story.
3)Mercury is karak of intelligency,education,thinking mind when it is placed in 10th house native may be very intelligent, may be scholar in many subjects,and full with mental strength. Through which native always interested to gain more knowledge,Native may be experts in tricky work,astrology,Mathematics.Overall native may be verylearned,courageous from mental strength, strong and powerful.
4)Mercury in 10th house consider auspicious regarding social Fame. As Mercury is karak for intelligency so native may be famous for his intelligency or such type of his intellectual work.
5)Mercury is karak of speech if Mercury is well placed then native may be good or honest in his speech regarding profession or if mercury is afflicted by Melific then native may be dishonest in speech regarding profession.In simple Mercury in 10th shows ur Sidhantavaditha in Your profession. In Genral native may be stick to his word.
6)A well place Mercury in 10th house indicating native may got success in very beginning in his ventures.Other wise native will success through his own efforts and intelligency.