[8] He has served as President (1997-1999) of the American College of Preventive Medicine[9][3] and as editor of the Annual Review of Public Health.

He also called attention to the underlying determinants of health, including wide disparities in the physical and social environments in which people live.

[18] Fielding was responsible for implementing the Los Angeles County "A B C" restaurant letter-grading system which has been widely emulated throughout the U.S.A.

[19] Other programs discourage tobacco use and encourage healthy nutrition, physical activity, and serving of appropriately-sized portions by restaurants.

[21] Fielding has also served as commissioner and vice-chair of the First 5 Los Angeles Commission, whose mission is to improve health and development of children 5 years of age and under, granting over $100 million annually.

[22] On March 27, 2014, Fielding announced that he would retire from the department and go back to UCLA "to help train future health leaders and do research on how we can be even more effective.

[4] He has authored over 300 peer-reviewed articles, chapters and editorials, publishing on a wide range of public health and preventive medicine issues.

[10] In 2016, Fielding started writing a monthly column for U.S. News & World Report on current topics in public health.

[25] Fielding has been a member of a number of national-level task forces that assess best evidence and make recommendations to improve the health of the public.

[26] Fielding is a former board member and former chair of the national Truth Initiative (formerly the American Legacy Foundation), which oversees $1 billion from the (year) tobacco settlement to end youth use of combustible cigarettes and other nicotine delivery devices.

They included portraits, landscape, furniture, textiles, pottery, ironwork, and other items, generally made in New England between 1680 and 1870.

[40] In 2024 he and his wife funded an endowed chair in climate change at the Fielding School of Public Health.

The inaugural holder of the Jonathan Fielding Chair in Climate Change and Public Health is UCLA FSPH Professor Michael Jerrett.