By one measure, Thomas Linguanti is among the most valuable lawyers in Big Law.

Consider this: Last year, he slashed a tax bill from $1.36 billion to $14 million for medical device manufacturer Medtronic plc.

As Linguanti prepares to brief the U.S. Court of Appeals for the Eighth Circuit on an Internal Revenue Service appeal on that big tax deduction decision, he is moving from one global law firm with an elite tax practice to another.