Olonga was born in Lusaka, Zambia. His father was Kenyan and his mother was Zimbabwean. He has two sisters and two brothers. His brother, Victor Olonga plays rugby in Zimbabwe, and became captain of the Zimbabwe national rugby union team. The former Kenyan minister Francis Masakhalia is his uncle.

After returning to Kenya, the family moved to Bulawayo in Zimbabwe. Olonga was educated at Rhodes Estate Preparatory School (REPS) and played cricket for the Partridges, the Zimbabwe national primary schools cricket team. He then attended Plumtree School, where he became head boy. He was involved in acting, athletics and rugby in addition to cricket. In a school cricket match against Brighton College, he scored 103 runs and took 8 wickets for 15 runs. He found a firm Christian faith in 1992 at a youth camp in Marondera.

Olonga made his debut in first-class cricket in March 1994, aged 17, playing for Matabeleland against Mashonaland in the Logan Cup. He took five wickets in the match, but had varied performances over the next couple of years. He continued to play domestic first-class cricket for Matabeleland until 1998–99, and then for Mashonaland A in 2001–02 and then for Manicaland in 2002–03.

He was not an obvious or automatic choice when he was selected to make his international debut for Zimbabwe in the Test against Pakistan at Harare in January 1995, (although Olonga could have been selected to play for Zimbabwe against Sri Lanka earlier in 1995, when David Brain and Eddo Brandes were absent due to injury, but he was found to be ineligible as he still held Kenyan nationality). Having given up his Kenyan citizenship, Olonga became the youngest player to represent Zimbabwe in international cricket, aged 18 years and 212 days.

A right arm fast bowler, Olonga was also the first black cricketer to play for Zimbabwe, and the third Zambian-born Test cricketer after Phil Edmonds and Neal Radford of England. Zimbabwe beat Pakistan by an innings and 64 runs, the team's first ever Test victory, mainly due to a double century from Grant Flower, and centuries from Andy Flower and Guy Whittall. Olonga took the wicket of Saeed Anwar in his first over, but he was no-balled once for throwing. With help from Dennis Lillee, he rebuilt his action before returning to international cricket.

He made his debut in ODIs playing against South Africa in October 1995. He was man of the match when he took his first 5-wicket haul (5–70) in Tests playing against India in October 1998, Zimbabwe's second Test victory, and he was the spearhead of the team that won Zimbabwe's first overseas Test, beating Pakistan at Peshawar in November 1998. He took a second and final Test 5-wicket haul (5–93) in a losing cause against Pakistan in November 2002.

Olonga played 30 Test matches for Zimbabwe, taking 68 wickets with a bowling average of 38.52, and 50 One Day Internationals, taking 58 wickets at an average of 34.08. He holds the record for the best bowling in an ODI by a Zimbabwean, with figures of 6–19 against England at Cape Town in 2000.

Cricket