Lavin began his career in the banking industry where he was an investor for more than 25 years. He held numerous director, vice chairman and chairman positions with several Chicago area banks. For over 15 years, he had his own financial consulting firm, Sheldon Lavin and Associates Inc., in downtown Chicago.
 
In 1970, Lavin became involved with Otto & Sons, the predecessor firm of OSI Industries LLC. Currently, he is chairman and CEO of the OSI Group LLC including OSI Industries, LLC and OSI International Foods LLC in the U.S., and OSI International Inc., which is the holding company for all of the OSI Group's international investments.  The OSI Group is also one of the largest shareholders and holds a seat on the board of directors of Marfrig Alimentos S/A in Brazil.  Marfrig is one of the largest fully integrated protein companies in the world.
 
Lavin led his company through expansion in North America and Europe in the 1970s, and in the 1980s expanded into South America and Taiwan. In the following decades, further growth included the Philippines, China, Australia, Japan, India and South Africa. Today, at age 81, Lavin is still actively pursuing further growth for his company with particular focus in Asia and Europe.

Lavin is a contributor and active in many charities including: Ronald McDonald House Charities (for which he is chairman of the Capital Campaign), the Inner City Foundation of Chicago, Jewish United Fund and numerous other Jewish charities, Evans Scholarship Fund, Boys and Girls Clubs of Chicago, United Negro College Fund, the National Multiple Sclerosis Society, and other national and local charities.