Mbithi's first feature film, KATI KATI, produced by award-winning German director Tom Tykwer, One Fine Day Films and Ginger Ink Productions, has won several international awards, including the International Federation of Film Critics (FIPRESCI) award in the Discovery Programme at the 2016 Toronto International Film Festival (TIFF). FIPRESCI described his work as 'an exciting and unique new voice in cinema'.

Kati Kati also went on to win the New Voices/New Visions Award Special Mention at the Palm Springs International Festival, the Filmpris at the 19th CinemAfrica Film Festival in Stockholm, the Emerging Filmmaker Award at the 2017 Minneapolis St Paul International Film Festival, and the Best East African Film award at the 2017 Africa Movie Viewers Choice Awards.

His entry for the 2015 edition of the 48 Hour Film Project, IT'S BEEN A WHILE, won the Audience Award and is one of Nairobi's featured selections.

Mbithi has directed ads for some of Kenya's most prominent brands, including Equity Bank, Safaricom, Barclays, Coca Cola, Centum, Oracle Kenya, Google Kenya, and the Simba Group.

As an artist, Mbithi has been a part of the highly acclaimed experimental art collective JUST A BAND. He worked on several video installations with the collective, including KUDISHNYAO!, hosted at the Rush Gallery in New York in 2012. His direction of music videos has earned him recognition from local and international press such as the New York Times, Fader, Huffington Post and Okay Africa, as well as being highlighted by Google during the launch of YouTube Kenya.