A term for an outstanding lawyer

Philadelphia lawyer

A lawyer knowledgeable in the most minute aspects of the law. M-W

legal beagle

(idiomatic) A skillful and adroit attorney. Wiktionary

virtuoso of the bar

virtuoso

A person who has special knowledge or skill in a field. Random House

On TV, he is primped and sexy, appealing to men and women, worshipped by all; an object of jealousy, perhaps, but also of respect; a virtuoso of the bar, fearless and shameless, smashing the prosecution's argument to pieces with the jackhammer of his wit... The Age of Reinvention

barrister

In the United States a fancy name for a lawyer or attorney. In Great Britain, there is a two-tier bar made up of solicitors who perform all legal tasks except appearance in court and barristers, who try cases. Some solicitors will "take the silk" (quaint expression) and become barristers. (See: solicitor) Gerald N. Hill and Kathleen T. Hill

An informal expression which is close to what you are looking for is legal eagle:

• (slang) a lawyer, esp. one regarded as highly skilled or ambitious

  • He made his reputation as a legal eagle as a prosecutor before entering private practice.

(yourdictionary.com)

The expression silver-tongued is also used to refer to a lawyer with persuasive speech:

Silver-tongued lawyer.