A $2m bounty was also announced on Abdul Rehman Makki, Mr Saeed’s brother-in-law and co-founder of Lashkar.
Both Jamaat-ud-Dawa and Lashkar-e-Taiba are blacklisted by the US.
The US announced the award for their capture or information leading to their capture, officials said.
The three-day rampage in November 2008 by 10 gunmen in Mumbai left 165 people dead. Nine of the attackers were also killed.
India blamed the Mumbai attacks on LeT, and India-Pakistan ties hit rock bottom.
The sole surviving gunman, Pakistani national Mohammad Ajmal Amir Qasab, was captured and sentenced to death by a court. His appeal is pending.
‘Most wanted’
Mr Saeed figures prominently on a list of “most wanted” given to Pakistan by India. Jamaat-ud-Dawa denies it operates as a front for militancy.
He was held after the Mumbai attacks but released without charge.
The US State Department’s Rewards for Justice website describes Mr Saeed as “a Pakistani citizen” with “red hair” and “brown eyes”.
“Hafiz Mohammad Saeed is a former professor of Arabic and engineering, as well as the founding member of Jamaat-ud-Dawa, a radical Deobandi Islamist organisation dedicated to installing Islamist rule over parts of India and Pakistan, and its military branch, Lashkar-e-Taiba,” the website says.
India welcomed the announcement of the reward.