Leaviss joined M&G in 1997, evolving the firm’s fixed-income team from a four-person unit into a global powerhouse with 40 specialists across London, Chicago, Singapore, and Paris. Beyond his formal role as Chief Investment Officer, he cultivated a unique voice through his 'Bond Vigilantes' blog and the 'Uncle Jim’s World of Bonds' podcast. He was known for explaining macroeconomic trends through unconventional metaphors, using everything from the gold-hoarding habits of J.R.R. Tolkien’s Smaug to the shrinking size of snack food packets to illustrate the realities of inflation and government debt.

His colleagues remember him as a mentor who possessed a rare ability to bridge the gap between technical expertise and public discourse. Stefan Isaacs, co-head of macro credit at M&G, described him as a formative leader who made bond markets engaging for a wider audience. After leaving M&G in 2024 to pursue the study of art history, Leaviss left behind a legacy of fiscal analysis that prioritized clarity and humor. The firm has opened a virtual book of condolences, with the family requesting that any memorial contributions be directed to Cancer Research UK.