The battle of Ambur (3 August 1749) was the first battle of the Second Carnatic War, and saw Anwar-ud-Din, the incumbent Nawab of the Carnatic, defeated and killed by an allied army formed by the new Nizam of Hyderabad, the French, and a claimant to the Nawabship of the Carnatic.
In 1748 the incumbent Nizam of Hyderabad, Nizam-ul-Mulk died, after nominating his grandson Muzaffar Jang as his heir. This appointment had been confirmed by the Mughal emperor, but Nizam-ul-Mulk's second son Nasir Jang was able to seize control of Hyderabad.
Muzaffar Jang soon found allies to support his claim. While attempting to gain allies amongst the Marathas he found Chanda Sahib, the son-in-law of a previous Nawab of the Carnatic, and a prisoner since 1741. With the help of the French governor of Pondicherry, Joseph Dupleix, Chanda Sahib was released. He was able to raise 3,500 troops of his own, while Dupleix provided him with 2,000 Sepoys and 400 European troops. Meanwhile Muzaffar Jang had been able to raise 30,000 troops of his own. The combined force of 36,000 men advanced towards Arcot, the capitol of the Carnatic.
The incumbent Nawab of the Carnatic, Anwar-ud-Din, had been appointed by Nizam-ul-Mulk, and if he had been able to hold for any length of time could have expected to receive help from Nasir Jang, who did later provide support for his son, but instead of holding out in Arcot, Anwar-ud-Din decided to advance towards the allies with his own 20,000 strong army.
The two sides met on 3 August 1749 at Ambur (or Amoor). Despite being outnumbered, the Carnatic forces held their own for some time, but eventually the disciplined French infantry tipped the balance. Anwar-ud-Din was killed in the battle, and on the following day Muzaffar Jang and Chanda Sahib entered Arcot. Chanda Sahib became the de-facto Nawab of the Carnatic, but Anwar-ud-Din's son Muhammed Ali escaped from the disaster and fled south to Trichinopoly, where he prepared to fight on.