Halas is best known for showing that the nanoscale internal and external morphology of noble metal nanoparticles controls their optical properties. She was the first person to introduce structural control into the colloidal synthesis of coinage metal nanoparticles to control their optical resonances, which are due to their collective electron oscillations known as plasmons. Her work has been the force that merged chemical nanofabrication with optics, giving rise to the field of Plasmonics. She pursues fundamental studies of coupled plasmonic systems as well as applications of plasmonics in many fields, including biomedicine, optoelectronics, chemical sensing, solar steam generation and water treatment, and plasmonic photocatalysis. She is the author of more than 400 refereed publications, has more than twenty-five issued patents, has presented more than 650 invited talks, and has been named as a Highly Cited researcher for the past decade (over 90,000 citations and H=148 on Web of Science, over 125,000 citations and H=168 on Google Scholar). She is co-founder of Syzygy Plasmonics, a company with over 100 employees that has developed a light-based chemical reactor for ambient-temperature ammonia cracking and methane reforming, using the photocatalyst particles originally invented in her laboratory. She is also co-founder of Nanospectra Biosciences, a company offering ultralocalized photothermal ablation therapies for cancer based on her nanoparticles.

Halas is a member of the National Academy of Engineering, the National Academy of Sciences, the Royal Danish Academy of Science and Letters, and the American Academy of Arts and Sciences. She is a recipient of the C. E. K. Mees Medal and the R.W. Wood Prize from the Optical Society of America, the Mildred Dresselhaus Prize for Nanoscience and Nanomaterials, the Frank Isakson Prize for Optical Effects in Solids, and the Julius Lilienfeld Prize of the American Physical Society, and the American Chemical Society Award in Colloid Chemistry. She is a Fellow of several professional societies: Optica, APS, SPIE, IEEE, MRS, the Royal Society of Chemistry (UK), the National Academy of Inventors (US) and the American Association for the Advancement of Science. She has been a National Security Science and Engineering Faculty Fellow (now called Vannevar Bush Fellow) of the U.S. Department of Defense and an advisor to the Mathematical and Physical Sciences Directorate of the National Science Foundation. She is currently a Hans Fischer Senior Fellow at the Technische Universität München, and she has been awarded three honorary doctorate degrees.