Mariga started his playing career at Ulinzi Stars he later crossed over to Tusker FC and then to Kenya Pipeline while still at school. The central midfielder was part of Kamukunji High School ‘Golden Boys’, alongside Dennis Oliech who won two consecutive National Championships in 2002 and 2003.
Mariga moved abroad in 2005 to play for Swedish third Division side Enköpings SK. a season later he signed for Helsingborgs IF. His success at Helsingborgs was immediate. He attracted interest from Portsmouth manager Harry Redknapp, Mariga looked set to sign for the Premier League team, but work permit issues held up the deal which was supposed to have cost around €2.7 million.
He moved to the Serie A club Parma initially on loan in August 2007. The Italian club had an option to buy him in the summer for a fee of 20 million Swedish kronor.
Mariga agreed to a four-year deal to keep him at Serie A side Parma for four years until the end of June 2012, after the club paid a transfer fee for Swedish Kronor 18 million (approx. 1.94 million euro). Mariga played 35 times for Parma in the Serie B during the 2008–2009 season scoring three times to help them back to Serie A for the 2009–10 season. In January 2010 he was set to sign for English club Manchester City of the Premier League, but he failed to obtain a work permit. He eventually obtained a UK work permit but only after the transfer window for the Premier League had closed. He missed out the chance to be the first player from the East African country to sign for a club in the top English league.
On 1 February 2010, the last day of the transfer window, Mariga moved to Inter in a co-ownership deal. The transfer fee was €5 million in a cash plus player deal which Parma got half the registration rights of Jonathan Biabiany (€2.5 million) and the loan of Luis Antonio Jiménez. Inter chairman Massimo Moratti hailed Mariga’s move as the “best thing that could have happened” to the club in the January transfer window. His debut at Inter was in the 1st leg of the 2009-10 Coppa Italia Semi-final against Fiorentina. Inter won the match 1–0. In March 2010 Mariga became the first Kenyan to play in the UEFA Champions League when he entered the field as a late substitute against Chelsea a record that is yet to be broken.
On 17 June 2010, Inter bought him outright and bought back Biabiany for €4.2 million each, which made Parma registered a “loss from co-ownership” of €800,000, as the retained profit of unsold half had decreased from €5 million to €4.2 million. However, if counting the profit from Biabiany, which Inter, in fact, paid Parma €10.9 million cash for Mariga plus the special loan of Biabiany. While Luis Antonio Jiménez originally included in the deal but collapsed after Inter lost its portion on 25 June.
At the start of the 2011–12 season Mariga was loaned out to La Liga club Real Sociedad. It meant Inter had a non-EU transfer quota which they used on winter signing Juan and Fredy Guarín (the other quota was obtained from Philippe Coutinho). After half a season back at Inter, he was loaned to Parma in the January 2013 transfer window and he scored his only goal against Lazio. In the next fixture, he was injured against Novara, which ruled him out for the rest of the season. He returned to Inter along with Biabiany at the end of the season at the request of manager Andrea Stramaccioni but was released by the club in May 2014.
On 4 September 2014, Mariga re-signed with Parma, the team he left to join Inter in 2010. He later moved to Latrina amd made a return to Spain signing for Real Oviedo.
He is a son to Noah Wanyama, an A.F.C. Leopards legend his younger brother Victor Wanyama is a dependable midfielder at Tottenham, while his other brothers Thomas and Sylvester have been at Kenyan Premier League sides. He has a sister and she has specialized in Basket ball.