The 23-year-old, who has toured Europe with Samoa and played in the Pacific Rugby Cup earlier this year for his country, made his Test debut for Samoa against Japan in Tokyo.
Muagututia - who is 6ft 2in and weights 17 stone - jetted into Sixways this week to join up with his new team-mates.
He said: "This is a great opportunity for me and a new start. It is exciting to join the Warriors and to play in England. I will play hard and for the future and hope to make a good impression with the supporters."
Head Coach Richard Hill was pleased to welcome new recruit Muagututia, but added the back row would need time to adjust to life in England.
"Richard is a young player who will be experiencing club rugby outside of Samoa for the very first time," he said.
"He has been on tour in Europe before, but this will be a big change of culture. We will initially give him time to settle in and acclimatise.
"In many ways, Richard is similar to Ravai Fatiaki, who we will also welcome after the Rugby World Cup. This is a big opportunity for him and if he can make an impression and prove himself then we will look to contract him for even longer.
"Richard is a talent and was very highly recommended by Brian Lima, who knows a good player after featuring in five World Cups. He is firmly regarded as a really big prospect for Samoa and one we believe can make big strides at Warriors."