Here, Mercury is naturally disposed towards symmetry & balance. So these natives can be excellent artists who have an intuitive understanding about the relationship between things, how to arrange them so that there is harmony. They can absolutely be musicians working on composing symphonies, producing mind-aligning beats, conducting an orchestra, or playing an instrument, especially wind instruments like the flute or clarinet… but any instrument is possible. They know which instruments go well together, they have a natural ear for different sounds, and could also have heightened sensitivity to sound. Naturally gifted with rhythm and comprehension of the mathematical patterns in well-produced music. Acoustics are a point of interest, the way sound moves in a space, and the way a space is designed overall, which can make them very particular about the way they arrange their space.
Similarly, Libra Mercury can be excellent drawers, painters, they understand proportion and correct placement, for that reason they can also excel in engineering or physics, anything that requires precise mathematics, like an architect who figures out exact measurements of a building so that it evenly distributes weight and can stand upright.
So Mercury in Libra tends to arrange things, make them beautiful, harmonious, balanced, even, take many things into consideration.
Libra Mercury is also likely to have siblings or a best friend, someone they spend time with frequently, and someone they make decisions with also, where they can send a question or a proposal and their close friend would weigh the options and help them come to a conclusion together, so Mercury in Libra may tend towards being very communicative, inquisitive, cooperative, not insistent on doing things by themselves, and even if they rather do things alone, they may have to learn how to work with others as a frequent theme in life.
Of course, Mercury in Libra also make certain judgments about fairness, they could take on the positions of judges in a courtroom, or grading student's work, or validating proof of concept, or acting as lawyers convincing the jury of their case, or seeking financial reparations for wrongdoing. Bottom line, one of Libra Mercury's roles is restoration of justice.
So they may have strong political opinions about how things should be done, how much money should be allocated… there are always conversations and decisions being made about how to do things better, how to make things fair and equitable.
Mercury in Libra can also find themselves in positions of mediation. For instance, they might be the person in the friend group that tries to bring everyone together and see all sides of a situation. If they feel someone is acting unjustly or disproportionately, they would say so and explain why. Libra Mercury is excellent in relating the logic of something, the panoply of reasons why they have come to their decision. So they can be convincing speakers who also take the time to hear out the other person's side to completion and genuinely take it into consideration. Thus, they might be charismatic, likable, approachable, fair, and chosen as representatives for a cause.
Also, Mercury in Libra is likely to enjoy strategy games, word games or math games. Chess, Checkers, Monopoly, Scrabble, Sudoku, matching games, dress-up games, engineering games… anything that gets their mind working on arranging things, moving them around, thinking carefully about their next move, planning. Libra Mercury obtains tremendous satisfaction from reaching consensus, doing the math to get to the right answer, arranging meeting times that work for everyone involved, coming to an agreement… when everything finally aligns and clicks into complete balance, regardless which discipline they get this from.
They might also have a particularly pleasant voice, which can make them naturally gifted singers… but they might lean towards podcasting, making and editing videos of themselves speaking, doing audiobook narration, reading out loud, or going to book clubs to discuss everyone's different perspectives on something they've read together. They could also be interested in sound healing, sound baths and overall good audio-visual quality. It's imperative that things are beautifully done.
Some Libra Mercury could have a natural talent in finance and accounting, balancing accounts, working with spreadsheets, reporting financial information or tracking movements in the stock markets. Again, they try to determine the correct value of a given company and see if it is undervalued or overvalued, and make a purchasing decision based on the facts.
On a more spiritual note, Mercury in Libra can take interest in nonviolent protests, nonviolent communication, Buddhist or Oriental mysticism practices of attaining peace through balancing one's subtle energy. Libra Mercury can practice yoga, meditation, contemplation, philosophy, and they're likely to work closely with a teacher, either as an engaged student or as a teacher's assistant. For Mercury in Libra, spirituality can be experienced through art, mathematics, physics, logic… seeing the beauty in numbers, in the grand architecture of life and its various precise formulae, like in the irrational number pie (3.14…), in the golden ratio, in the Vitruvian man, in marvelous works of art, in the consistent language of nature.