Yes, congruent triangles are always similar. Congruence is actually a special, stricter case of similarity.
Why this is true
Two triangles are similar if their corresponding angles are equal and their corresponding sides are proportional (in the same ratio). Two triangles are congruent if they are identical in both shape and size — meaning their corresponding angles are equal AND their corresponding sides are exactly equal in length.
Since equal side lengths are simply a special case of proportional side lengths (with a scale factor, or ratio, of 1:1), every congruent triangle automatically satisfies the definition of similarity. In other words, congruent triangles are similar triangles with a similarity ratio of 1.
The key distinction
- Similar triangles: same shape, but can be different sizes (angles match, sides are proportional).
- Congruent triangles: same shape AND same size (angles match, sides are equal).
So congruence implies similarity, but similarity does not imply congruence. Two triangles can be similar (same angles, proportional sides) while being different sizes — for example, a small triangle and a larger scaled-up copy of it are similar but not congruent unless the scale factor happens to be exactly 1.
A useful analogy
Think of similarity as being about "family resemblance" (same shape) and congruence as being an exact "twin" (same shape and same size). All twins resemble each other, but not everyone who resembles someone is their twin. Likewise, all congruent triangles are similar, but not all similar triangles are congruent.
This relationship is a standard result taught in geometry courses worldwide and follows directly from the formal definitions of congruence (SSS, SAS, ASA, AAS, HL criteria) and similarity (AA, SSS~, SAS~ criteria).