The pair join the previously cast David Strathairn in the show, which follows a team of ordinary people who develop brain anomalies and receive unusual mental and physical abilities.
Yoba will play Bill Harken, a former FBI agent who possesses superhuman strength and speed, while Mennell will appear as Nina Theroux, a team member who can manipulate people's emotions.
"Malik and Laura are perfect additions to an already impressive ensemble cast. They both have great intensity and charisma," said SyFy executive Mark Stern. "We look forward to seeing them breathe life into the complex characters of Harken and Nina."
Yoba previously played astronaut Ted Shaw on space travel drama Defying Gravity, while Mennell appeared in 2009 film Watchmen.
Production on the show's pilot is due to begin next month in Toronto, under the direction of former Lost executive producer Jack Bender.