In 1847 he was one of a partnership approved by the territorial legislature to build the first bridge across the Fox River in Oshkosh.

In 1850 he was elected and served a single one-year term in the Wisconsin State Assembly as a Free Soil Party member.

In the town of Oshkosh, Eastman began dealing in general merchandise, and for many years he was in partnership with L. M. Miller.

He was appointed US postmaster of Oshkosh by the administration of Democratic President James K. Polk in that same year, serving until 1849 in the patronage position.

The administration and patronage appointments changed after election in 1848 of Whig Zachary Taylor as President of the United States.

In 1850, he was elected to the Winnebago County seat in the Wisconsin Assembly, succeeding Democrat Leonard P. Crary, as a Free Soiler.

[7] In the summer of 1851, following the end of the legislative session, Eastman opened a bookstore and stationery store in Oshkosh.

[8] Eastman also continued to serve as Postmaster until 1861, when the newly elected Republican administration of Abraham Lincoln took office and made its own appointments.

[9] In 1854, he joined such figures as James Duane Doty, Mason Darling, Theodore Conkey and his old partner Lucas Miller as a director of the newly re-organized Wisconsin Farmers' Insurance Company.