In this paper, we propose and study a novel Time—frequency‐domain iterative multiuser detector (TF‐IMUD) for the multicarrier direct‐sequence code‐division multiple‐access (DS‐CDMA) systems employing both time (T)‐domain and frequency (F)‐domain spreading, which, for brevity, are referred to as the TF/MC DS‐CDMA systems. This novel TF‐IMUD consists of a set of T‐domain soft‐input soft‐output MUDs (SISO‐MUDs) and a set of F‐domain SISO‐MUDs, where information is exchanged between the T‐domain and F‐domain through two multiuser interference (MUI) cancellation units. The T‐domain and F‐domain SISO‐MUDs are operated under the maximum likelihood (ML) principles, and they are facilitated to be implemented using parallel signal processing techniques. In this paper, the complexity of the TF‐IMUD and the bit error rate (BER) performance of the TF/MC DS‐CDMA systems employing the proposed TF‐IMUD are investigated and also compared with the other existing MUD schemes, including the optimum ML‐MUD and the joint/separate minimum mean‐square error (MMSE)‐MUDs. Our study and simulation results show that the TF‐IMUD is capable of achieving nearly the same BER performance as the optimum ML‐MUD, but at significantly lower complexity. Copyright © 2010 John Wiley & Sons, Ltd.