The 31-year-old, who has represented the Proteas in eight Test matches, five ODIs and five T20Is, will join Kent ahead of the T20 Blast campaign as well as eight first-class fixtures.
Muthusamy played a starring role in South Africa's Test series victory India in November - there first in the country in 25 years - hitting maiden Test century in the second Test in Guwahati.
The left-arm spinner also showed his allround capabilities with 11 wickets in the first Test against Pakistan in Lahore before the series in India.
"I'm looking forward to the challenge of playing County Championship & Vitality Blast cricket for the first time at a Club with a big history," Muthusamy said.
"I've heard a lot of good things about Kent from my teammates that have played there before, and I'm relishing the opportunity to make contributions with bat and ball in a Kent shirt."
Kent's Director of Cricket, Simon Cook, added: "Sen is an extremely versatile player, able to bat across the middle and lower order in Championship cricket.
"He will also be an asset for us on late-season surfaces that are usually more conducive to spin.
"In the Vitality Blast, he also provides left-handed hitting options at the back end of an innings as well as an economical spin option through the middle overs as we look to be competitive in multiple formats this season.
"Overseas players contribute in many ways beyond on-field performance. Sen's experience will be invaluable in helping our young players develop into better cricketers.
"In particular, the time he spends with Jaydn Denly, also a left-handed batter and left-arm spinner, will be crucial in his development."
All-rounder Senuran Muthusamy scored his maiden Test ton (109) and Marco Jansen smashed a brisk 93 (91) to boost South Africa to 480 all out on Day Two of the second Test.
There was double delight for South Africa after Proteas Women's captain Laura Wolvaardt and men's spinner Senuran Muthusamy scooped the ICC player of the month awards for October.
The Proteas started the defence of their World Test Championship with a drawn series against Pakistan.
Senuran Muthusamy wants to embrace the challenge of putting in consistent performances at the highest level as he chases a place in the Proteas squad for next year's T20 World Cup.
