Rick Warren invited Kagame – who has ruled Rwanda since 2000 to speak "as we join our Rwandan brothers and sisters in remembering the 1994 genocide against the Tutsi and thank God together for the renewal the country has experienced over the last 25 years".
However, Kagame is a controversial figure that has also been blamed for denying Rwandans basic human rights.
Aristide Rwigara is the younger brother of Diane Rwigara, who ran against Kagame for president and was imprisoned along with her mother and sister after he came to power.
Ms Rwigara was barred from running in presidential elections and spent over a year in prison before being acquitted.
Aristide Rwigara told the Los Angeles Times: "Why would he give attention to someone who has closed thousands of churches and who has consistently denied human rights to his own people?
"This cannot go unchallenged. Warren is a global figure, and if you want to wear the mantle of spiritual leadership, why would you do this?
"I used to think he was the real deal, and then I found out that he backed the government — a government that stifles all manner of opposition, that has no humanity."
Kagame told Warren at the church that he had the difficult task of reintegrating society and uniting the population after the genocide.
"We had a tragic situation where over one million people died," Kagame said.
"Every individual had their own struggles and problems to deal with. The starting point was to create an environment to make sure individuals did not feel alone."
Kagame held an interactive discussion with close to 700 members of Saddleback Church after the service.
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