Dumbarton chief executive Gilbert Lawrie said: "We are thankful to Motherwell for agreeing terms."
Lawrie told his club website that these would "be beneficial to Dumbarton FC as Nicky's career develops".
As part of the deal, midfielder Jordan Halsman's loan from the Scottish Premier League club to Dumbarton has been extended until the end of the season.
This is a win-win situation for all concerned
Motherwell head of youth development Gordon Young
Motherwell head of youth development Gordon Young said: "Motherwell FC are delighted to secure the services of Nicholas Devlin and also are particularly satisfied at the reciprocal agreement we have struck up with Dumbarton FC as a result of excellent dialogue between the two clubs.
"It is hoped that this can be repeated and a number of avenues are being explored which would benefit both parties.
"Having conducted the deal and experienced the dialogue between his parents, it's apparent we are signing the correct type of person as well as a dedicated footballer.
"This is a win-win situation for all concerned and thanks is due to all who contributed in the process."
Devlin's performances have led to his selection as captain of Scotland's Under-18 side and a call-up to the Under-19 squad.
Source: BBC Sport
Source: BBC Sport