He will star opposite DCI Banks actress Andrea Lowe in the show, the broadcaster announced today.
Love Life, which has been written by Lark Rise to Candleford and Conviction scribe Bill Gallagher, focuses on the relationship between Collier's character Joe and Lowe's Lucy.
After Lucy pressures him to settle down, Joe goes travelling for a year - but when he returns, he discovers that Lucy is now pregnant after an affair with her married boss.
Gregor Fisher has joined the cast as Lucy's father Will, while Alexander Armstrong will play her boss Dominic and Sophie Thompson will star as Dominic's wife Penny.
Kieran O'Brien, Lisa Millett, Sorcha Cusack and Naomi Bentley have also landed roles in the three-part series.
BBC One is also developing a separate project called Love Life, which features stars including David Tennant, Billie Piper and Jenny Agutter.