Let’s look at important things here –
Mercury - Mercury represents communication skills, marketing, calculative ability, younger siblings, hobbies, skills with hands, intelligence, quick decision making, logical thinking, youthfulness etc.
Magha - Magha is nakshatra of Kings, Authority and Authoritative Positions. It is also nakshatra of celebrities. For more information on Magha, please check this - https://www.astrosaxena.com/maghnaksh.
Leo - As Magha is a part of Leo, Leo sign and its representations become important. Leo is 5th sign of zodiac belt, hence it represents the things associated with 5th house of horoscope like Love, Creativity, Arts, Being on Stage etc. Besides that, Leo is basically the Lion. This is the sign of feeling like King or Queen. Also, it is a sign of independence, Confidence, Ego, Self Esteem etc. Leo is consisted of 2 and half Nakshatra namely Magha, Purva-Phalguni and Uttara-Phalguni. Leo's lord is Sun..
Sun - As Sun rules Leo, Sun's position and dignity is important to know about the overall functioning of any planet in Magha/Leo.
Ketu - As Magha is ruled by Ketu, Ketu's position and dignity will also have an important role in functioning and results of any planet in Magha.
Houses Involved – Also, we can’t afford to forget the houses involved as a planet can be ruling different houses and sitting in different house for every person as per ascendant and planet’s position. To know overall affect, we have to consider the houses involved as those areas of life are being impacted.
Interpretation of Mercury in Magha Nakshatra – Dignity-wise, Mercury is in good dignity here in Sun ruled sign and Ketu ruled Nakshatra. As Magha represents the true Leo Nature of being in Royal Position, Authority or be like a King and as Mercury is all about Communications, this position can be best represented by someone who is working as messenger of Govt/high authority or working as spokesperson of Govt. A Govt Counselor or Lawyer can also be seen with this position. It can also indicate someone who gains his kingly status or authority through his business and communication skills. As Leo and Mercury both represent interests and creativity, they can be very creative and skillful. They can also gain their authority through their creative interests. As Magha is ruled by Ketu which represents research and Mercury is all about collection of information, these people can be very good at any type of research work. It can make them inclined towards interests like occult and spirituality. At the same time, if Mercury is relationship oriented planet for them then their relations can suffer from ego clashes and dissatisfaction.
Role of Sun – Sun's placement is important to guide Mercury in right direction, being Leo's lord.
Role of Ketu - Likewise, Ketu's placement is important to guide Mercury in right direction, being Magha's lord.
Other Factors – And of course, we need to consider conjunction, aspects, house lordship, house position and dashas etc to know the exact results of Mercury in Magha. So, we always need to take a holistic view of chart rather than just 1 planetary position.
Conclusion – So, this is how I see Mercury in Magha Nakshatra can work in a chart.
Hope this helps. Please post any comment or query you may have.