* Mulligan represents Trump company executive Allen Weisselberg

* High-profile former clients include ex-FIFA executive Chuck Blazer

July 1 (Reuters) - The indictment of a top official at former U.S. President Donald Trump's company marks a critical shift from probe to prosecution by Manhattan District Attorney Cyrus Vance Jr.

New York lawyer Mary Mulligan could play a key role in what happens next.

Mulligan, a former federal prosecutor turned criminal defense attorney, is representing Allen Weisselberg https://www.reuters.com/world/us/trump-organization-cfo-expected-be-charged-thursday-wsj-2021-06-30, the Trump Organization's longtime chief financial officer. After a nearly three-year investigation, Vance's office unsealed tax charges against Weisselberg on Thursday.

Weisselberg was charged in the 15-count indictment with avoiding taxes on $1.7 million of income and pleaded not guilty to second-degree larceny and other charges.

Mulligan, who declined to comment on her multi-year representation of Weisselberg, is no stranger to high-profile assignments.

She previously defended an ex-Lehman Brothers broker https://www.reuters.com/article/insidertrading-devlin/broker-who-stole-business-secrets-from-wife-avoids-prison-idINDEE82M0OX20120323 who stole corporate secrets from his executive wife and shared them with friends, and a South African pilot who was arrested alongside https://www.reuters.com/article/us-usa-crime-bout/accomplice-to-arms-dealer-bout-handed-five-year-prison-term-idUSBRE84M1KV20120523 Russian arms dealer Viktor Bout in an undercover sting by U.S. agents posing as Colombian guerrillas looking to buy weapons.

She also represented Chuck Blazer https://www.reuters.com/article/us-soccer-blazer/banned-former-fifa-executive-chuck-blazer-dies-idUSKBN19Y08J, the former FIFA executive committee member who pleaded guilty to racketeering, wire fraud and money laundering for accepting bribes in the bidding process for the 1998 World Cup in France and the 2010 World Cup in South Africa.

Mulligan was an assistant U.S. attorney for the Southern District of New York from 1997 to 2002. In that role, she investigated and prosecuted fraud, corruption and financial crimes cases, according to her LinkedIn profile.

She joined law firm Friedman Kaplan Seiler & Adelman in 2006, after a stint in-house at Universal Music Group. Her practice includes defending clients against allegations of money laundering, insider trading, corruption, campaign violations and various types of fraud.

Weisselberg is a close Trump confidant, making his cooperation potentially crucial to any future case against Trump himself.

Trump, a Republican, released a statement on Thursday calling the prosecution a "witch hunt." (Reporting by Caroline Spiezio; Editing by David Bario, Daniel Wallis and Noeleen Walder)