David Hitlin received his B.A. (1963), M.A. (1965), and Ph.D. (1968) from Columbia University. His doctoral research with C.S. Wu used high-resolution muonic X-ray spectroscopy to determine the shapes and sizes of deformed nuclei. He served as an Instructor at Columbia from 1967 to 1969. Although trained in experimental nuclear physics, he shifted to elementary particle physics, joining the Stanford Linear Accelerator Center (SLAC) as a Research Associate in the Schwartz/Wojcicki group. Appointed Assistant Professor of Physics at Stanford in 1972, he helped construct a large spectrometer for precision studies of weak decays and interactions of neutral kaons and designed a stopping pion and muon channel for the planned HEPL superconducting linac. Using the kaon spectrometer, he participated in measurements of CP violation through charge asymmetries in semileptonic kaon decays, determined vector and scalar decay form factors consistent with current algebra predictions, and conducted precision studies of kaon decay modes, branching ratios, and photon spectra. He later became co-Spokesman, with Robert Morse, of Experiment E92, which used the spectrometer to study K_L^0p interactions with a rapid-cycling bubble chamber.

In 1975 he joined the Richter group, participating in e⁺e⁻ annihilation studies at SPEAR. He led construction of the Mark II detector liquid-argon electromagnetic calorimeter and served as co-Spokesman. In 1978 he conceived and became founding Spokesman of the Mark III experiment, optimized for exclusive state reconstruction. Mark III carried out influential studies of charm meson weak decays and hadronic systems produced in J/ψ and ψ′ decays, including measurements of absolute D meson branching fractions and precise determinations of D meson lifetimes.

Hitlin moved to Caltech in 1979 as an Associate Professor and was promoted to Professor in 1986. He was a co-founder of the SLD experiment at the Stanford Linear Collider and served as System Manager for its liquid-argon calorimeter. Through the BES collaboration in Beijing, he continued studies of J/ψ, charm, and τ physics, contributing to the most precise measurement of the τ-lepton mass and resolving an apparent discrepancy with Standard Model expectations. He played a central role in securing approval of the PEP-II asymmetric e⁺e⁻ collider at SLAC and served for six years as founding Spokesman of the BABAR experiment. BABAR established CP-violating asymmetries in B⁰ meson decays, providing the first experimental confirmation that the Cabibbo-Kobayashi-Maskawa mechanism explains observed CP violation. This work provided the scientific foundation recognized by the 2008 Nobel Prize in Physics awarded to Kobayashi, Maskawa, and Nambu. BABAR has produced more than 600 refereed publications and remains a cornerstone of flavor-physics research. He later played a leading role in the proposed SuperB project, although it was ultimately not funded.

In 2010 he joined the Mu2e experiment at Fermilab, which searches for charged-lepton flavor violation through muon-to-electron conversion in aluminum with sensitivity four orders of magnitude beyond previous limits. He is Deputy System Manager for the electromagnetic calorimeter. In 2016 he joined the Light Dark Matter eXperiment (LDMX) at SLAC and serves as Technical Coordinator for its search for hidden-sector dark matter particles. Hitlin was Principal Investigator of the Caltech High Energy Physics grant from 1994 to 2010. He has received a DOE Outstanding Junior Investigator Award, is a Fellow of the American Physical Society, and was co-recipient of the 2016 APS W. K. H. Panofsky Prize in Experimental High Energy Physics.

He served three terms as Chairman of the SLAC Users Organization. He has served on numerous advisory and review bodies, including the Program Advisory Committees of SLAC, Fermilab, Cornell, and Brookhaven; the Argonne High Energy Physics Advisory Panel; the DOE Technical Advisory Panel on the University Program; the Fastbus Standards Committee; the High Energy Physics Advisory Panel to DOE and NSF; and the Fermi Research Alliance Board of Trustees.