Sheldon began his legal career as a general litigator in a small firm and has been practicing labor and employment law since the early 1970s. In the late 1960s, he was the Executive Director of Delaware's neighborhood legal services program, then known as Community Law Service. During the 1970s, he pioneered the specialty of labor and employment law in Delaware and along with Barry Willoughby began Young Conaway's Employment Law Section in 1981.
His prominence in the field has been recognized repeatedly. Chambers USA - America's Leading Lawyers for Business ranked him first in its ratings of Delaware Employment Lawyers representing Management, in each of its USA editions to date. In its 2007 study of "Management, Labour and Employment," Who's Who Legal, a UK publication, named him as 1 of 352 "experts in labour and employment law" internationally who "can truly be considered leaders in the field." He was again selected by Who's Who Legal for 2009 "as being among the world's pre-eminent Management Labour & Employment lawyers." He has also been listed in The Best Lawyers In America® for twenty-five years and in 2007, the first year that Delaware listings were published, he was recognized by Delaware Super Lawyers®.
At the 2004 American Bar Association Convention, Sheldon became the first Delaware lawyer inducted as a Fellow of the College of Labor and Employment Lawyers. Election as a Fellow is described as "the highest recognition by one's colleagues of sustained outstanding performance in the profession, exemplifying integrity, dedication and excellence."