Matsudaira Tadamasa (松平 忠昌, 21 January 1598 – 20 September 1645) was an early to mid-Edo period Japanese samurai, and daimyō.

He was noted for his skill in the martial arts, and accompanied Hidetada during the Siege of Osaka, where he was frustrated that he would not be allowed to participate in the battle due to his youth.

He strongly petitioned Hidetada to perform his genpuku ceremony before the start of the Osaka summer campaign, and Hidetada agreed, granting him a kanji from his name and Court rank of Senior Fifth Rank, Lower Grade and the courtesy title was Iyo-no-kami.

In 1634, he accompanied Shōgun Tokugawa Iemitsu to Kyoto, and Fukui Domain reached its peak kokudaka of 505,600 koku.

In 1637, he was disappointed that no order came to lead his troops during the Shimabara Rebellion, so he visited the battle in a private capacity with only twelve retainers.