Uehara was born as Tatsuoka Shinaga in Miyakonojō, Hyūga Province (present-day Miyazaki Prefecture), as the second son of a samurai in the service of Satsuma Domain.

He graduated from the Imperial Japanese Army Academy in 1879 with Akiyama Yoshifuru as one of his classmates, and his speciality was military engineering.

In August 1892, Uehara was appointed aide-de-camp to Prince Arisugawa Taruhito and also served as an instructor at the Army Staff College.

Uehara was on the staff of the IJA 1st Army (commanded by General Nozu Michitsura) and was promoted to lieutenant colonel in September 1894 while in Korea.

In May, he was reassigned to the 2nd Bureau of the General Staff and in March 1896 was assigned to accompany Prince Fushimi Sadanaru as part of Japan's official delegation to the coronation of Tsar Nicholas II of Russia.

With the start of the Russo-Japanese War, Uehara became chief-of-staff of the Japanese Fourth Army (commanded by General Nozu Michitsura).

The appointment had the support of General Terauchi Masatake, and Uehara specifically requested an assignment far from Tokyo, so that the Choshu-dominated Army Ministry would be unable to interfere.

Since the civilian government was pursuing a tight fiscal policy, it soon came into conflict with the army, which was demanding an increase in funding for another two infantry divisions.