The speech was the keynote address at the 2009 National Conference on Volunteering and Service.
"We're calling on Americans to make service not just something they do in their spare time, but something they do all the time," said Obama.
Other speakers at the event included Speaker of the House Nancy Pelosi and California governor Arnold Schwarzenegger.
Earlier today, Obama joined Shriver and about 500 volunteers at Bret Harte Elementary School, where they refurbished the school's playground.
The new playground includes an edible garden has a farmer's market stand where kids and seniors can sell vegetables to raise money for the school.
President Barack Obama announced an initiative known as "United We Serve" in a video message last week. The president is urging people to aid the nation's recovery by volunteering at schools, hospitals, and around the community.
Several government officials across the country are performing community service today in order to promote the campaign.