Can a colleague provide a letter of recommendation or do we need someone senior for that?

A colleague can provide a letter of recommendation if they know your work and skills well, but it’s usually better to get one from someone senior - such as a supervisor, manager, or professor. Recommendations from senior individuals carry more weight because they can speak to your abilities from a position of authority.

If your colleague is senior to you or has directly supervised your work, their letter can still be strong. Otherwise, aim for a recommender with a higher or more authoritative role.