In 1982, Rasanga entered the public service in the Ministry of Agriculture as a supplies officer in charge of National Agricultural laboratories. To advance his knowledge in procurement, he joined the Kenya Institute of Administration where he attained a Diploma in Supplies Management in 1985. Rasanga proceeded to work as a supplies officer in different districts and was promoted to senior procurement officer in charge of procurement and materials management. In 2000, Rasanga went back to university to pursue a law degree and graduated in 2003 from the University of Nairobi with a Bachelor of Law. He was admitted as an advocate of the High Court in 2005.
Political career
Rasanga entered politics in 2013 when he vied for Governor for Siaya County. The Orange Democratic Movement selected Rasanga as its candidate after a disputed nomination between Oburu Odinga and Oduol. He won the 4 Marchgeneral election but his election was nullified by the Court of Appeal in Kisumu on 23 August. Rasanga clinched the governorship in a subsequent by-election and became the first governor-elect of Siaya County. In 2017 he won the gubernatorial seat again flooring the then public accounts committee chair and Rarieda Mp Nicholas Odero Gumbo.