The centre-back, 28, is out of contract at the end of the season, having played in each of Livingston's 33 top-flight games this term.

Gallagher was a youth player at Celtic and had spells with Clyde and Dundee before joining Livingston in 2014.

"We have been a long-term admirer of Declan," said Motherwell manager Stephen Robinson.

"We are very pleased to have confirmed him for next season."

Gallagher has made more than 160 appearances for the West Lothian club, and helped them to successive promotions from League One.

That came after he served 16 months in prison after being found guilty of assaulting a man outside a hotel in Blantyre.